**NCERT Class 11 Mathematics Chapter 10 Conic Sections** **Solutions,** **NCERT Solutions For Class 11 Maths, NCERT Class 11 Mathematics Chapter 10 Conic Sections Notes **to each chapter is provided in the list so that you can easily browse throughout different chapter **NCERT Class 11 Mathematics Chapter 10 Conic Sections****Notes** and select needs one.

**NCERT Class 11 Mathematics Chapter 10 Conic Sections**

**NCERT Class 11 Mathematics Chapter 10 Conic Sections**Also, you can read the CBSE book online in these sections Solutions by Expert Teachers as per (CBSE) Book guidelines. **NCERT****Class 11 Mathematics Chapter 10 Conic Sections Textual Question Answer. **These solutions are part of NCERT All Subject Solutions. Here we have given

**for All Subject, You can practice these here.**

**Solutions****NCERT Class 11 Mathematics Chapter 10 Conic Sections****Conic Sections**

**Conic Sections****Chapter – 10**

Exercise 10.1 |

**In each of the following Exercises 1 to 5, find the equation of the circle with**

**1. centre (0,2) and radius 2**

Ans: The equation of a circle with centre (h, k) and radius r is given as

(x – h)² + (y – k)² = r²

It is given that centre (h, k) = (0, 2) and radius (r) = 2

Therefore, the equation of the circle is

(x + 0)² + (y – 2)² = 2²

x² + y² + 4 – 4y = 4

x² + y² – 4y = 0.

**2. centre (-2,3) and radius 4**

Ans: The equation of a circle with centre (h, k) and radius r is given as

(x – h)² + (y – k)² = r²

It is given that centre (h, k) = (- 2, 3) and radius (r) = 4

Therefore, the equation of the circle is

(x + 2)² + (y – 3)² = (4)²

x² + 4x + 4 + y² – 6y + 9 = 16

x² + y² + 4x – 6y – 3 = 0.

Ans: The equation of a circle with centre (h, k) and radius r is given as

(x – h)² + (y – k)² = r²

Therefore, the equation of the circle is

144x² – 144x + 36 + 144y² – 72y + 9 – 1 = 0

144x² – 144x + 144y² – 72y + 44 = 0

36x² – 36x + 36y² – 18y + 11 = 0

36x² + 36y² – 36x – 18y + 11 = 0

**4. centre (1,1) and radius √2**

Ans: The equation of a circle with centre (h, k) and radius r is given as

(x – h)² + (y – k)² = r²

It is given that centre (h, k) = (1, 1) and radius (r) = √2

Therefore, the equation of the circle is

(x – 1)² + (y – 1)² = (√2)²

x² – 2x + 1 + y² – 2y + 1 = 2

x² + y² – 2x – 2y = 0

**5. centre (- a, – b) and radius √a² – b²)**

Ans: The equation of a circle with centre (h, k) and radius r is given as

(x – h)² +(y – k)² = r²

It is given that centre (h, k) =(- a, – b) and radius (r) = √a² – b²

Therefore, the equation of the circle is

(x + a)² + (y + b)² = (√a² – b²)²

x² + 2ax + a² + y² + 2by + b² = a² – b²

x² + y² + 2ax + 2by + 2b² = 0

In each of the following Exercises 6 to 9, find the centre and radius of the circles.

**6. (x + 5)² + (y – 3)² = 36**

Ans: The equation of the given circle is (x + 5)² + (y – 3)² = 36

(x + 5)² + (y – 3)² = 36

⇒ {x – (- 5)}² + (y – 3)² = 6² , which is of the form (x – h)² + (y – k)² = r² ,where h = – 5 k = 3 and r = 6

Thus, the centre of the given circle is (-5, 3), while its radius is 6.

**7. x² + y² – 4x – 8y – 45 = 0**

Ans: The equation of the given circle is x² + y² – 4x – 8y – 45 = 0.

x² + y² – 4x – 8y – 45 = 0

⇒ (x² – 4x) + (y² – 8y) = 45

⇒{x² – 2(x)(2) + 2²} + {y² – 2(y)(4)+4²} – 4 – 16 = 45

⇒ (x – 2)² + (y – 4)² = 65

⇒ (x – 2)² + (y – 4)² = (√65)² , which is of the form (x – h)² + (y – k)² = r² where h = 2, k = 4 and r = √65

Thus, the centre of the given circle is (2, 4), while its radius is √65.

**8. x² + y² – 8x + 10y – 12 = 0**

Ans: The equation of the given circle is x² + y² – 8x + 10y – 12 = 0.

x² + y² – 8x + 10y – 12=0

⇒ (x² – 8x) + (y² + 10y) = 12

⇒{x² – 2(x)(4) + 4²} + {y² + 2(y)(5) + 5²} – 16 – 25 = 12

⇒ (x – 4)² + (y + 5)² = 53

⇒ (x – 4)² + {y – (- 5)}² = (√53)² ,which is of the form (x – h)² + (y – k)² = r² , where h = 4, k = – 5,

and r = √53

Thus, the centre of the given circle is ( 4 ,- 5) while its radius is √53

**9. 2x² + 2y² – x = 0.**

Ans: The equation of the given circle is 2x² + 2y² – x = 0 .

2x² + 2y² – x = 0

⇒ (2x² – x) + 2y² = 0

**10. Find the equation of the circle passing through the points (4,1) and (6,5) and whose centre is on the line 4x + y = 16**

Ans: Let the equation of the required circle be (x – h)² +(y – k)² = r²

Since the circle passes through points (4, 1) and (6, 5),

( 4 – h)² +(1 – k)² =r² …(1)

(6 – h)² +(5 – k)² = r² … (2)

Since the centre (h, k) of the circle lies on line 4x + y = 16 ,

4h + k = 16 (3)

From equations (1) and (2), we obtain

( 4 – h)² +(1 – k)² =(6 – h)² +(5 – k)²

⇒ 16 – 8h + h² +1 – 2k + k²=36 – 12h + h² +25 – 10k+k²

⇒ 16 – 8h+1 – 2k = 36 – 12h + 25 – 10k

⇒ 4h + 8k = 44

⇒ h + 2k = 11 … (4)

On solving equations (3) and (4), we obtain h = 3 and k = 4

On substituting the values of h and k in equation (1), we obtain

(4 – 3)² +(1 – 4)² = r²

⇒ (1)² + (- 3)² = r²

⇒ 1 + 9 = r²

⇒ r² = 10

⇒ r = √10

Thus, the equation of the required circle is

(x – 3)² + (y – 4)² = (√10)²

x² – 6x + 9 + y² – 8y + 16 = 10

x² + y² – 6x – 8y + 15 = 0.

**11. Find the equation of the circle passing through the points (2,3) and (-1,1) and whose centre is on the line x – 3y – 11 = 0**

Ans: Let the equation of the required circle be (x – h)² + (y – k)² = r²

Since the circle passes through points (2, 3) and ( – 1,1),

( 2 – h)² +(3 – k)² =r² …(1)

( – 1 – h)² +(1 – k)² = r²…(2)

Since the centre (h, k) of the circle lies on line x – 3y – 11 = 0,

h – 3k =11…(3)

From equations (1) and (2), we obtain

(2 – h)² + (3 – k)² = (- 1 – h)² + (1- k)²

⇒ 4 – 4h + h² + 9 – 6k + k² = 1 + 2h + h² + 1 – 2k + k²

⇒ 4 – 4h + 9 – 6k = 1 + 2h + 1 – 2k

⇒ 6h + 4k =11…(4)

On solving equations (3) and (4), we obtain

On substituting the values of h and k in equation (1), we obtain

Thus, the equation of the required circle is

4x² – 28x + 49 + 4y² + 20y + 25 = 130

4x² + 4y² – 28x + 20y – 56 = 0

4(x² + y² – 7x + 5y – 14) = 0

x² + y² – 7x + 5y – 14 = 0

**12. Find the equation of the circle with radius 5 whose centre lies on x-axis and passes through the point (2,3).**

Ans: Let the equation of the required circle be (x – h)² +(y – k)² = r ²

Since the radius of the circle is 5 and its centre lies on the x-axis, k = 0 and r = 5

Now, the equation of the circle becomes (x – h)² + y² = 25 .

It is given that the circle passes through point (2, 3).

∴ (2 – h)² + 3² = 25

⇒ (2 – h)² = 25 – 9

⇒ (2 – h)² = 16

⇒ 2 – h = ±√16 = ± 4

If 2 – h = 4 then h = – 2

If 2 – h = – 4 then h = 6

When h = – 2, the equation of the circle becomes

(x + 2)² + y² = 25

x² + 4x + 4 + y² = 25

x² + y² +4x – 21=0

When h = 6 the equation of the circle becomes

(x – 6)² + y² = 25

x² – 12x + 36 + y² = 25

x² +y² – 12x + 11 = 0

**13. Find the equation of the circle passing through (0,0) and making intercepts a and b on the coordinate axes.**

Ans: Let the equation of the required circle be (x – h)² +(y – k)²= r²

Since the circle passes through (0, 0),

(0 – h)² +(0 – k)² = r²

⇒ h² + k² = r²

The equation of the circle now becomes (x – h)² + (y – k)² = h² + k²

It is given that the circle makes intercepts a and b on the coordinate axes. This means that the circle passes through points (a, 0) and (0, b) Therefore,

(a – h)² + (0 – k)² = h² + k²…. (1)

(0 – h)² + (b – k)² = h² + k² …..(2)

From equation (1), we obtain

a² – 2ah + h² + k² = h² + k²

⇒ a² – 2ah = 0

⇒ a(a – 2h) = 0

⇒ a = 0 or (b – 2k)=0

However, b ≠ 0; hence, (b – 2k) = 0 ⇒h = a/2

From equation (2), we obtain

h² +b² – 2bk + k² = h² + k²

⇒ b² – 2bk = 0

⇒ b( b – 2k)=0

⇒ b = 0 or(b – 2k) = 0

However, b ≠ 0; hence, (b – 2k)=0⇒ k = b/2

Thus, the equation of the required circle is

⇒ 4x² – 4ax + a² + 4y² – 4by + b² = a² + b²

⇒ 4x² + 4y² – 4ax – 4by = 0

⇒ x² + y² – a x – by = 0

**14. Find the equation of a circle with centre (2,2) and passes through the point (4,5)**

Ans: The centre of the circle is given as (h, k) = (2, 2) .

Since the circle passes through point (4, 5), the radius (r) of the circle is the distance between the points (2, 2) and (4, 5).

∴ r = √(2 – 4)² + (2 – 5)² = √(- 2)² + (- 3)² = √4 + 9 = √13

Thus, the equation of the circle is

(x – h)² + (y – k)² = r²

(x – 2)² + (y – 2)² = (√13)²

x² – 4x + 4 + y² – 4y + 4 = 13

x² + y² – 4x – 4y – 5 = 0

**15. Does the point (-2.5, 3.5) lie inside, outside or on the circle x² + y² = 25′**

Ans: The equation of the given circle is x² + y² = 25

x² + y² = 25

⇒(x – 0)² +(y – 0)² = 5² , which is of the form (x – h)² + (y – k)² = r²,where h = 0, k = 0 and r = 5

∴ Centre = (0, 0) and radius = 5

Distance between point (- 2.5,3.5) and centre (0, 0)

= √(- 2.5 + 0)² + (3.5 + 0)²

= √6.25 + 12.25)

= √18.5

= 4.3 (approx.)<5

Since the distance between point ( – 2.5,3.5) and centre (0, 0) of the circle is less than the radius of the circle, point ( – 2.5,3.5) lies inside the circle.

Exercise 10.2 |

**In each of the following Exercises 1 to 6, find the coordinates of the focus, axis of the parabola, the equation of the directrix and the length of the latus rectum.**

**1. y² = 12x.**

Ans: The given equation is y² = 12x

Here, the coefficient of x is positive. Hence, the parabola opens towards the right.

On comparing this equation with y² = 4ax , we obtain

4a =12 ⇒ a=3

∴ Coordinates of the focus = (a, 0) = (3, 0)

Since the given equation involves y² the axis of the parabola is the x-axis.

Equation of directrix, x = – a i.e., x = – 3 i.e., x + 3 = 0

Length of latus rectum = 4a = 4 x 3 = 12

**2. x² = 6y.**

Ans: The given equation is x² = 6y

Here, the coefficient of y is positive. Hence, the parabola opens upwards.

On comparing this equation with x² = 4ay, we obtain

∴ Coordinates of the focus = (0, a) =

Since the given equation involves x², the axis of the parabola is the y-axis.

Equation of directrix,

Length of latus rectum = 4a= 6

**3. y² = – 8x.**

Ans: The given equation is y² = – 8x

Here, the coefficient of x is negative. Hence, the parabola opens towards the left.

On comparing this equation with y² = – 4ax we obtain

– 4a =-8 ⇒ a=2

∴ Coordinates of the focus = (- a, 0) = (- 2, 0)

Since the given equation involves y² the axis of the parabola is the x-axis.

Equation of directrix, x = a i.e., x = 2

Length of latus rectum = 4a= 8

**4. x² = – 16y.**

Ans: The given equation is x² = – 16y

Here, the coefficient of y is negative. Hence, the parabola opens downwards.

On comparing this equation with x² = – 4ay we obtain

-4a=-16 ⇒ a = 4

∴ Coordinates of the focus = (0, – a) = (0, – 4)

Since the given equation involves x², the axis of the parabola is the y-axis.

Equation of directrix, y= a i.e., Y = 4

Length of latus rectum = 4a = 16

**5. y² = 10x.**

Ans: The given equation is y² = 10x

Here, the coefficient of x is positive. Hence, the parabola opens towards the right.

On comparing this equation with y² = 4ax we obtain

Since the given equation involves y² the axis of the parabola is the x-axis.

Equation of directrix,

Length of latus rectum = 4a = 10

**6. x² = – 9y.**

Ans: The given equation is x² = – 9y

Here, the coefficient of y is negative. Hence, the parabola opens downwards.

On comparing this equation with x² = – 4ay, we obtain

∴ Coordinates of the focus =

Since the given equation involves x² the axis of the parabola is the y-axis.

Equation of directrix

Length of latus rectum = 4a= 9.

In each of the Exercises 7 to 12, find the equation of the parabola that satisfies the given conditions:

**7. Focus (6,0); directrix x = – 6**

Ans: Focus (6, 0); directrix, x = – 6

Since the focus lies on the x-axis, the x-axis is the axis of the parabola.

Therefore, the equation of the parabola is either of the form y² = 4ax or

y² = – 4ax

It is also seen that the directrix, x = – 6 is to the left of the y-axis, while the focus (6, 0) is to the right of the y-axis.

Hence, the parabola is of the form y² = 4ax

Here, a = 6

Thus, the equation of the parabola is y² = 24x.

**8. Focus (0,-3); directrix y = 3.**

Ans: Focus = (0, -3); directrix y = 3

Since The focus lies on the y-axis, the y-axis is the axis of the parabola.

Therefore, the equation of the parabola is either of the form x² = 4ay or

x² = – 4ay.

It is also seen that the directrix, y = 3 is above the x-axis, while the focus

(0, -3) is below the x-axis. Hence, the parabola is of the form x² = – 4ay

Here, a = 3

Thus, the equation of the parabola is x² = – 12y.

**9. Vertex (0,0); focus (3,0).**

Ans: Vertex (0, 0); focus (3, 0)

Since the vertex of the parabola is (0, 0) and the focus lies on the positive x-axis, x-axis is the axis of the parabola,

while the equation of the parabola is of the form y² = 4ax

Since the focus is (3, 0), a = 3 .

Thus, the equation of the parabola is y² = 4 x 3 x x, i.e., y² = 12x

**10. Vertex (0,0); focus (-2,0).**

Ans: Vertex (0, 0) focus (-2, 0)

Since the vertex of the parabola is (0, 0) and the focus lies on the negative x-axis, x-axis is the axis of the parabola,

while the equation of the parabola is of the form y² = – 4ax

Since the focus is (-2, 0), a = 2

Thus, the equation of the parabola is y² = – 4(2) x i.e., y² = – 8x.

**11. Vertex (0,0) passing through (2,3) and axis is along x-axis.**

Ans: Since the vertex is (0, 0) and the axis of the parabola isthe x-axis, the equation of the parabola is either of the

form y² = 4ax or y² = – 4ax

The parabola passes through point (2, 3), which lies in the first quadrant.

Therefore, the equation of the parabola is of the form y² = 4ax while point

(2, 3) must satisfy the equation y² = 4ax

Thus, the equation of the parabola is

**12. Vertex (0,0), passing through (5,2) and symmetric with respect to y-axis.**

Ans: Since the vertex is (0, 0) and the parabola is symmetric about the y-axis, the equation of the parabola is either of the

formx²= 4ay or x² = – 4ay

The parabola passes through point (5, 2), which lies in the first quadrant.

Therefore, the equation of the parabola is of the form x² = 4ay while point

(5, 2) must satisfy the equation x² = 4ay

Thus, the equation of the parabola is

2x² = 25y

Exercise 10.3 |

**In each of the Exercises 1 to 9, find the coordinates of the foci, the vertices, the length of the major axis, the minor axis, the eccentricity and the length of the latus rectum of the ellipse.**

Ans: The given equation is

Therefore, the major axis is along the x-axis, while the minor axis is along the y-axis.

On comparing the given equation with

we obtain a = 6 and b = 4

Therefore

The coordinates of the foci are (2√5, 0) and (- 2√5, 0)

The coordinates of the vertices are (6, 0) and ( – 6,0)

Length of major axis = 2a= 12

Length of minor axis = 2b= 8

Ans: The given equation is

Therefore, the major axis is along the y-axis, while the minor axis is along the x-axis.

On comparing the given equation with

we obtain b = 2 and a = 5

∴ c = √a² – b² = √25 – 4 = √21

Therefore,

The coordinates of the foci are (0, √21) and (0, – √21)

The coordinates of the vertices are (0, 5) and (0, – 5)

Length of major axis = 2a = 10

Length of minor axis = 2b = 4

Length of latus rectum

Ans: The given equation is

On comparing the given equation with

,we obtain a = 4 and b = 3

:. c = √a² – b²) = √16 – 9 = √7

Therefore,

The coordinates of the foci are (±√7,0)

The coordinates of the vertices are (±4,0)

Length of major axis = 2a = 8

Length of minor axis = 2b = 6

Ans: The given equation is

Therefore, the major axis is along the y-axis, while the minor axis is along the x-axis.

On comparing the given equation with

we obtain b = 5 and a = 10

:. c = √a² – b²) = √100 – 25 = √75 = 5√3

Therefore,

The coordinates of the foci are (0, ± 5√3)

The coordinates of the vertices are (0,±10).

Length of major axis = 2a = 20

Length of minor axis = 2b = 10

Ans: The Given equation is

Therefore, the major axis is along the x-axis, while the minor axis is along the y-axis.

On comparing the given equation with

, we obtain a = 7 and b = 6

∴ c = √a² – b²) = √49 – 36 = √13

Therefore,

The coordinates of the foci are (±√13, 0)

The coordinates of the vertices are ( ± 7 ,0).

Length of major axis = 2a = 14

Length of minor axis = 2b= 12

Ans: The given equation is

Therefore, the major axis is along the y-axis, while the minor axis is along the x-axis.

On comparing the given equation with

we obtain b = 10 and a = 20

∴ c = √a² – b²) = √400 – 100 = √300 = 10√3

Therefore,

The coordinates of the foci are (0, ±10√3)

The coordinates of the vertices are (0,±20)

Length of major axis = 2a = 40

Length of minor axis = 2b= 20

**7. 36x² + 4y² = 144.**

Ans: The given equation is 36x² + 4y² = 144

It can be written as

36x² + 4y² = 144

Therefore, the major axis is along the y-axis, while the minor axis is along the x-axis.

On comparing equation (1) with

, we obtain b = 2 and a = 6.

∴ c = √a² – b²) = √36 – 4 = √32 = 4√2

Therefore,

The coordinates of the foci are (0, ±4√2)

The coordinates of the vertices are (0, ± 6)

Length of major axis = 2a = 12

Length of minor axis = 2b = 4

Eccentricity,

Length of latus rectum

**8. 16x² + y² = 16.**

Ans: The given equation is 16x² + y² = 16

It can be written as

16x² + y² = 16

Therefore, the major axis is along the y-axis, while the minor axis is along the x-axis

On comparing equation (1) with

we obtain b = 1 and a = 4

∴ c = √a² – b²) = √16 – 1 = √15

Therefore,

The coordinates of the foci are (0, ±√15)

The coordinates of the vertices are (0, ± 4)

Length of major axis = 2a = 8

Length of minor axis = 2b = 2

**9. 4x² + 9y² = 36.**

Ans: The given equation is 4x² + 9y² = 36

It can be written as

4x² + 9y² = 36

Therefore, the major axis is along the x-axis, while the minor axis is along the y-axis.

On comparing the given equation with

we obtain a = 3 and b = 2

∴ c = √a² – b²) = √9 – 4 = √5

Therefore,

The coordinates of the foci are (±√5, 0)

The coordinates of the vertices are (± 3 ,0)

Length of major axis = 2a = 6

Length of minor axis = 2b = 4

In each of the following Exercises 10 to 20,find the equation for the ellipse that satisfies the given conditions:

**10. Vertices (± 5,0), foci (±4, 0).**

Ans: Vertices (±5, 0), foci (±4, 0)

Here, the vertices are on the x-axis

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, a = 5 and c = 4

It is known that a² = b² + c²

∴ 5² = b² + 4²

⇒ 25 = b² + 16

⇒ b² = 25 – 16

⇒ b = √9 = 3

Thus, the equation of the ellipse is

**11. Vertices (0, ±13), foci (0, ±5).**

Ans: Vertices (0, ±13), foci (0, ±5).

Here, the vertices are on the y-axis.

Therefore, the equation of the ellipse will be of the form

,where a is the semi-major axis.

Accordingly, a = 13 and c = 5

Accordingly, a = 13 and c = 5

It is known that a² = b² + c²

∴ 13² = b² + 5²

⇒ 169 = b² + 25

⇒ b² = 169 – 25

⇒ b = √144 = 12

Thus, the equation of the ellipse is

**12. Vertices (± 6, 0), foci (±4, 0).**

Ans: Vertices ( ± 6 ,0) foci ( ± 4 ,0)

Here, the vertices are on the x-axis.

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, a = 6 c = 4

It is known that a² = b² + c²

∴ 6² = b² + 4²

⇒ 36 = b² + 16

⇒ b² = 36 – 16

⇒ b = √20

Thus, the equation of the ellipse is

**13. Ends of major axis (± 3, 0), ends of minor axis ( ds of (0,±2)**

Ans: Ends of major axis (± 3 ,0) ends of minor axis (0, ± 2)

Here, the major axis is along the x-axis.

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, a = 3 and b = 2

Thus, the equation of the ellipse is

**14. Ends of major axis (0,±√5), ends of minor axis (± 1,0)**

Ans: Ends of major axis (0, ±√5) , ends of minor axis (±1 ,0)

Here, the major axis is along the y-axis.

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, a = √5 and b = 1

Thus, the equation of the ellipse is

**15. Length of major axis 26, foci (±5, 0)**

Ans: Length of major axis = 26; foci = (±5, 0).

Since the foci are on the x-axis, the major axis is along the x-axis.

Therefore, the equation of the ellipse will be of the form

,where a is the semi-major axis

Accordingly, 2a =26 ⇒ a=13 and c = 5

It is known that a² = b² + c²

∴ 13² = b² + 5²

⇒ 169 = b² + 25

⇒ b² = 169 – 25

⇒ b = √144 = 12

Thus, the equation of the ellipse is

**16. Length of minor axis 16, foci (0, ± 6)**

Ans: Length of minor axis = 16; foci = (0, ±6).

Since the foci are on the y-axis, the major axis is along the y-axis.

Therefore, the equation of the ellipse will be of form

,where a is the semi-major axis.

Accordingly, 2b =16 ⇒ b=8 and c = 6

It is known that a² = b² + c²

∴ a² = 8² + 6² = 64 + 36 = 100

⇒ a = √100 = 10

Thus, the equation of the ellipse is

**17. Foci (±3, 0), a = 4**

Ans: Foci ( ± 3 ,0) a = 4

Since the foci are on the x-axis, the major axis is along the x-axis.

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, c = 3 and a = 4

It is known that a² = b² + c²

∴ 4² = b² + 3²

⇒16 = b² + 9

⇒ b² = 16 – 9 = 7

Thus, the equation of the ellipse is

**18. b = 3 c = 4 centre at the origin; foci on the x axis.**

Ans: It is given that b = 3, c = 4 centre at the origin; foci on the x axis.

Since the foci are on the x-axis, the major axis is along the x-axis.

Therefore, the equation of the ellipse will be of the form

where a is the semi-major axis.

Accordingly, b = 3, c = 4

It is known that a² = b² + c²

∴ a² = 3² + 4² = 9 + 16 = 25

⇒ a = 5

Thus, the equation of the ellipse is

**19. Centre at (0,0), major axis on the y-axis and passes through the points (3, 2) and (1,6).**

Ans: Since the centre is at (0, 0) and the major axis is on the y-axis, the equation of the ellipse will be of the form

Where, a is the semi-major axis

The ellipse passes through points (3, 2) and (1, 6). Hence,

On solving equations (2) and (3), we obtain b² = 10 and a² = 40

Thus, the equation of the ellipse is

**20. Major axis on the x-axis and passes through the points (4,3) and (6,2).**

Ans: Since the major axis is on the x-axis, the equation of the ellipse will be of the form

Where, a is the semi-major axis

The ellipse passes through points (4, 3) and (6, 2). Hence,

On solving equations (2) and (3), we obtain a² = 52 and b² = 13

Thus, the equation of the ellipse is

Exercise 10.4 |

**In each of the Exercises 1 to 6, find the coordinates of the foci and the vertices, the eccentricity and the length of the latus rectum of the hyperbolas.**

Ans: The given equation a

On comparing this equation with the standard equation of hyperbola i.e.

we obtain a = 4 and b = 3

We know that a² + b² = c²

∴ c² = 4² + 3² = 25

⇒ c = 5

Therefore,

The coordinates of the foci are ( ± 5 ,0).

The coordinates of the vertices are ( ± 4 ,0)

Length of latus rectum

Ans: The given equation is

On comparing this equation with the standard equation of hyperbola i.e

we obtain a = 3 and b = √27

We know that a² + b² = c²

∴ c² = 3² + (√27)² = 9 + 27 = 36

⇒ c = 6

Therefore,

The coordinates of the foci are (0, ± 6)

The coordinates of the vertices are (0, ± 3)

Length of latus rectum

**3. 9y² – 4x² = 36.**

Ans: The given equation is 9y² – 4x² = 36

It can be written as

9y – 4x² = 36

On comparing equation (1) with the standard equation of hyperbola i.e.

we obtain a = 2 and b = 3

We know that a² + b² = c²

∴ c² = 4 + 9 = 13

⇒ c = √13

Therefore,

The coordinates of the foci are (0, ± √13)

The coordinates of the vertices are (0, ± 2)

Length of latus rectum

**4. 16x² – 9y² = 576.**

Ans: The given equation is 16x² – 9y² = 576

It can be written as

16x² – 9y² = 576

On comparing equation (1) with the standard equation of hyperbola i.e.,

, we obtain a = 6 and b = 8

We know that a² + b² = c² .

∴ c² = 36 + 64 = 100

⇒ c = 10

Therefore,

The coordinates of the foci are ( ± 10 ,0)

The coordinates of the vertices are ( ± 6 ,0).

Length of latus rectum

**5. 5y² – 9x² = 36.**

Ans: The given equation is 5y² – 9x² = 36

On comparing equation (1) with the standard equation of hyperbola i.e.

**2. We know that a² + b² = c²**

Therefore, the coordinates of the foci are

The coordinates of the vertices are

Length of latus rectum

**6. 49y² – 16x² = 784.**

Ans: The given equation is 49y² – 16x² = 784

It can be written as

49y² – 16x² = 784

On comparing equation (1) with the standard equation of hyperbola i.e.,

we obtain a = 4 and b = 7

we know that a² + b² = c²

∴ c² = 16 + 49 = 65

⇒c = √65

The coordinates of the foci are (0, ± √65)

The coordinates of the vertices are (0, ± 4)

Length of latus rectum

In each of the Exercises 7 to 15, find the equations of the hyperbola satisfying the given conditions.

**7. Vertices (±2,0), foci (±3,0).**

Ans: Vertices (± 2 ,0), foci ( ± 3 ,0)

Here, the vertices are on the x-axis.

Therefore, the equation of the hyperbola is of the form

Since the vertices are ( ± 2 ,0), a = 2

Since the foci are ( ± 3 ,0) c = 3 .

We know that a² + b² = c² .

∴ 2² + b² = 3²

b² = 9 – 4 = 5

Thus, the equation of the hyperbola is

**8. Vertices (0, ±5), foci (0,±8).**

Ans: Vertices (0, ± 5) foci (0, ± 8)

Here, the vertices are on the y-axis.

Therefore, the equation of the hyperbola is of the form

Since the vertices are (0, ± 5) a = 5

Since the foci are (0, ± 8) c = 8

We know that a² + b² = c²

∴ 5² + b² = 8²

b² = 64 – 25 = 39

Thus, the equation of the hyperbola is

**9. Vertices (0, ±3), foci (0, ±5)**

Ans: Vertices (0, ± 3) foci (0, ± 5)

Here, the vertices are on the y-axis.

Therefore, the equation of the hyperbola is of the form

Since the vertices are (0, ± 3) a = 3 .

Since the foci are (0, ± 5) c = 5

We know that a² + b² = c²

∴ 3² + b² = 5²

⇒ b² =25 â€” 9=16

Thus, the equation of the hyperbola is

**10. Foci (±5, 0), the transverse axis is of length 8.**

Ans: Foci ( ± 5 ,0) the transverse axis is of length 8.

Here, the foci are on the x-axis.

Therefore, the equation of the hyperbola is of the form

Since the foci are ( ± 5 ,0) c = 5

Since the length of the transverse axis is 8, 2a =8 ⇒ a=4 .

We know that a² + b² = c²

∴ 4² + b² = 5²

⇒ b² =25 â€” 16=9

Thus, the equation of the hyperbola is

**11. Foci (0, ±13), the conjugate axis is of length 24.**

Ans: Foci (0, ± 13) the conjugate axis is of length 24.

Here, the foci are on the y-axis.

Therefore, the equation of the hyperbola is of the form

Since the foci are (0, ± 13) c = 13

Since the length of the conjugate axis is 24, 2b =24 ⇒ b=12

We know that a² + b² = c²

∴ a² + 12² = 13²

⇒ a² =169 – 144 = 25

Thus, the equation of the hyperbola is

**12. Foci (± 3√5, 0) the latus rectum is of length 8.**

Ans: Foci (± 3√5, 0), the latus rectum is of length 8.

Here, the foci are on the x-axis.

Therefore, the equation of the hyperbola is of the form

Since the foci are (± 3√5, 0), c = ± 3√5 .

Length of latus rectum = 8

⇒ b² = 4a

We know that a² + b² = c²

∴ a² + 4a = 45

⇒ a² + 4a – 45 = 0

⇒ a² +9a – 5a – 45 = 0

⇒ (a + 9) (a – 5)=0

⇒ a = – 9,5

Since a is non-negative, a = 5

∴ b² = 4a = 4 × 5 = 20

Thus, the equation of the hyperbola is

**13. Foci (±4, 0), the latus rectum is of length 12.**

Ans: Foci ( ± 4 ,0) the latus rectum is of length 12.

Here, the foci are on the x-axis.

Therefore, the equation of the hyperbola is of the form

Since the foci are ( ± 4 ,0), c = 4 .

Length of latus rectum = 12

⇒ b² = 6a

We know that a² + b² = c²

∴ a² + 6a = 16

⇒ a² + 6a – 16=0

⇒ a² + 8a – 2a – 16=0

⇒ (a + 8) (a – 2)=0

⇒ a = – 8, 2

Since a is non-negative, a = 2 .

∴ b² = 6a = 6 × 2 = 12

Thus, the equation of the hyperbola is

**14. vertices (± 7,0), e = 4/3.**

Ans: Vertices ( ± 7 ,0),

Here, the vertices are on the x-axis

Therefore, the equation of the hyperbola is of the form

Since the vertices are ( ± 7 ,0), a = 7

It is given that

We know that a² + b² = c²

Thus, the equation of the hyperbola is

**15. Foci (0, ± √10), passing through (2,3).**

Ans: Foci (0, ±√10), passing through (2, 3)

Here, the foci are on the y-axis.

Therefore, the equation of the hyperbola is of the form

Since the foci are (0, ±√10),c = √10

We know that a² + b² = c²

∴ a² + b² = 10

⇒ b² =10 – a² …(1)

Since the hyperbola passes through point (2, 3),

From equations (1) and (2), we obtain

⇒ 9(10 – a²) – 4a² = a² (10 – a²)

⇒ 90 – 9a² – 4a² = 10a² – a⁴

⇒ a⁴ – 23a² + 90 = 0

⇒ a⁴ – 18a² – 5a² + 90 = 0

⇒ a² (a² – 18) – 5(a² – 18) = 0

⇒ (a² – 18)(a² – 5) = 0

⇒ a² = 18 or 5

In hyperbola, c > a i.e., c² > a²

∴ a² = 5

⇒ b² = 10 – a² = 10 – 5 = 5

Thus, the equation of the hyperbola is

Miscellaneous Exercise on Chapter 10 |

**1. If a parabolic reflector is 20 cm in diameter and 5 cm deep, find the focus.**

Ans: The origin of the coordinate plane is taken at the vertex of the parabolic reflector in such a way that the axis of the reflector is along the positive x-axis.

This can be diagrammatically represented as

The equation of the parabola is of the form y² = 4ax (as it is opening to the right).

Since the parabola passes through point A (10, 5), 10² = 4a(5)

⇒ 100 = 20a

Therefore, the focus of the parabola is (a, 0) = (5, 0) , which is the mid – point of the diameter.

Hence, the focus of the reflector is at the mid – point of the diameter.

**2. An arch is in the form of a parabola with its axis vertical. The arch is 10 m high and 5 m wide at the base. How wide is it 2 m from the vertex of the parabola?**

Ans: The origin of the coordinate plane is taken at the vertex of the arch in such a way that its vertical axis is along the positive y – axis.

This can be diagrammatically represented as

The equation of the parabola is of the form x² = 4ay (as it is opening upwards).

It can be clearly seen that the parabola passes through point

Therefore, the arch is in the form of a parabola whose equation is

Hence, when the arch is 2 m from the vertex of the parabola, its width is approximately 2.23 m.

**3. The cable of a uniformly loaded suspension bridge hangs in the form of a parabola. The roadway which is horizontal and 100 m long is supported by vertical wires attached to the cable, the longest wire being 30 m and the shortest being 6 m. Find the length of a supporting wire attached to the roadway 18 m from the middle.**

Ans: The vertex is at the lowest point of the cable. The origin of the coordinate plane is taken as the vertex of the parabola,

while its vertical axis is taken along the positive y-axis. This can be diagrammatically represented as

Here, AB and OC are the longest and the shortest wires, respectively, attached to the cable.

DF is the supporting wire attached to the roadway, 18 m from the middle.

Here, AB = 30m OC = 6 m, and

The equation of the parabola is of the form x² = 4ay (as it is opening upwards).

The coordinates of point A are (50,30 â€” 6)= (50, 24) .

Since A (50, 24) is a point on the parabola,

(50)² = 4a(24)

The x-coordinate of point D is 18.

Hence, at x = 18

6(18)² = 625y

⇒ y = 3.11 (approx)

∴ DE = 3.11m

DF = DE + EF = 3.11m + 6m = 9.11m

Thus, the length of the supporting wire attached to the roadway 18 m from the middle is approximately 9.11 m.

**4. An arch is in the form of a semi-ellipse. It is 8 m wide and 2 m high at the centre. Find the height of the arch at a point 1.5 m from one end.**

Ans: Since the height and width of the arc from the centre is 2 m and 8 m respectively, it is clear that the length of the major axis is 8 m, while the length of the semi-minor axis is 2 m.

The origin of the coordinate plane is taken as the centre of the ellipse, while the major axis is taken along the x-axis. Hence, the semi-ellipse can be diagrammatically represented as

The equation of the semi-ellipse will be of the form

where a is the semi-major axis

Accordingly, 2a =8 ⇒ a = 4

b = 2

Therefore, the equation of the semi-ellipse is

Let A be a point on the major axis such that AB = 1.5m

Draw AC ⏊ ОВ.

OA = (4 â€” 1.5) m = 2.5m

The x-coordinate of point C is 2.5.

On substituting the value of x with 2.5 in equation (1), we obtain

⇒ y² = 2.4375

⇒ y = 1.56 (approx.)

∴ AC = 1.56m

Thus, the height of the arch at a point 1.5 m from one end is approximately 1.56 m.

**5. A rod of length 12 cm moves with its ends always touching the coordinate axes. Determine the equation of the locus of a point P on the rod, which is 3 cm from the end in contact with the x-axis.**

Ans: Let AB be the rod making an angle θ with OX and P (x, y) be the point on it such that AP = 3 cm.

Then, PB = AB – AP = (12 – 3) cm = 9 cm [AB = 12 cm]

From P, draw PQ ⏊ OY and PR ⏊ OX.

Since, sin² θ + cos³ θ = 1

Thus, the equation of the locus of point P on the rod is

**6. Find the area of the triangle formed by the lines joining the vertex of the parabola x² = 12y to the ends of its latus rectum.**

Ans: The given parabola is x² = 12y

On comparing this equation with x² = 4ay we obtain 4a =12 ⇒ a=3

∴ The coordinates of foci are S (0, a) = S (0, 3)

Let AB be the latus rectum of the given parabola.

The given parabola can be roughly drawn as

At y = 3 , x² =12(3) ⇒ x² =36 ⇒ x = ± 6

∴ The coordinates of A are ( – 6,3) , while the coordinates of B are (6, 3).

Therefore, the vertices of triangle OAB are Ο (0, 0), A ( – 6,3) , and B (6, 3).

Thus, the required area of the triangle is 18 unit².

**7. A man running a racecourse notes that the sum of the distances from the two flag posts from him is always 10 m and the distance between the flag posts is 8 m. Find the equation of the posts traced by the man.**

Ans: Let A and B be the positions of the two flag posts and P(x, y) be the position of the man. Accordingly, PA + PB = 10.

We know that if a point moves in a plane in such a way that the sum of its distances from two fixed points is constant, then the path is an ellipse and this constant value is equal to the length of the major axis of the ellipse.

Therefore, the path described by the man is an ellipse where the length of the major axis is 10 m, while points A and B are the foci.

Taking the origin of the coordinate plane as the centre of the ellipse, while taking the major axis along the x-axis, the ellipse can be diagrammatically represented as

The equation of the ellipse will be of the form

where a is the semi-major axis

Accordingly, 2a =10 ⇒ a=5

Distance between the foci (2c) = 8

⇒ c = 4

On using the relation c = √a² – b² , we obtain

4 = √25 – b²

⇒ 16 = 25 – b²

⇒ b² = 25 – 16 = 9

⇒ b = 3

Thus, the equation of the path traced by the man is

**8. An equilateral triangle is inscribed in the parabola y² = 4 ax, where one vertex is at the vertex of the parabola. Find the length of the side of the triangle.**

Ans: Let OAB be the equilateral triangle inscribed in parabola y² = 4ax

Let AB intersect the x-axis at point C.

Let OC = k

From the equation of the given parabola, we have y² =4ak ⇒ y = ± 2√ak

∴ The respective coordinates of points A and B are (k, 2√ak) and (k, – 2√ak)

AB = CA + CB = 2√ak + 2√ak = 4√ak

Since OAB is an equilateral triangle, OA² = AB²

∴ k² + (2√ak)² = (4√ak)²

⇒ k² + 4ak = 16ak

⇒ k² = 12ak

⇒ k = 12a

∴ AB = 4√ak = 4√a × 12a = 4√12a² = 8√3a

Thus, the side of the equilateral triangle inscribed in parabola y² = 4ax is 8√3a