NCERT Solutions for Class 11 Maths Chapter 11- Conic Sections Exercise 11.4

NCERT Solutions have been carefully compiled and developed as per the latest CBSE syllabus. NCERT Solutions contain a detailed step-by-step explanation of all the problems that are present in the NCERT textbook. The Exercise 11.4 of NCERT Solutions for Class 11 Maths Chapter 11- Conic Sections is based on the following topics:

  1. Hyperbola
    1. Eccentricity
    2. Standard equation of Hyperbola
    3. Latus rectum

The NCERT Solutions for Class 11 Maths enhance topics with engaging math activities that strengthen the concepts further. Each question of the exercise has been carefully solved for the students to understand, keeping the examination point of view in mind.

Download PDF of NCERT Solutions for Class 11 Maths Chapter 11- Conic Sections Exercise 11.4

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Solutions for Class 11 Maths Chapter 11 – Exercise 11.4

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.

1. x2/16 – y2/9 = 1

Solution:

Given:

The equation is x2/16 – y2/9 = 1 or x2/42 – y2/32 = 1

On comparing this equation with the standard equation of hyperbola x2/a2 – y2/b2 = 1,

We get a = 4 and b = 3,

It is known that, a2 + b2 = c2

So,

c2 = 42 + 32

=25

c = 5

Then,

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

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

Eccentricity, e = c/a = 5/4

Length of latus rectum = 2b2/a = (2 × 32)/4 = (2×9)/4 = 18/4 = 9/2

2. y2/9 – x2/27 = 1

Solution:

Given:

The equation is y2/9 – x2/27 = 1 or y2/32 – x2/272 = 1

On comparing this equation with the standard equation of hyperbola y2/a2 – x2/b2 = 1,

We get a = 3 and b = 27,

It is known that, a2 + b2 = c2

So,

c2 = 32 + (27)2

= 9 + 27

c2 = 36

c = 36

= 6

Then,

The coordinates of the foci are (0, 6) and (0, -6).

The coordinates of the vertices are (0, 3) and (0, – 3).

Eccentricity, e = c/a = 6/3 = 2

Length of latus rectum = 2b2/a = (2 × 27)/3 = (54)/3 = 18

3. 9y2 – 4x2 = 36

Solution:

Given:

The equation is 9y2 – 4x2 = 36 or y2/4 – x2/9 = 1 or y2/22 – x2/32 = 1

On comparing this equation with the standard equation of hyperbola y2/a2 – x2/b2 = 1,

We get a = 2 and b = 3,

It is known that, a2 + b2 = c2

So,

c2 = 4 + 9

c2 = 13

c = 13

Then,

The coordinates of the foci are (0, 13) and (0, –13).

The coordinates of the vertices are (0, 2) and (0, – 2).

Eccentricity, e = c/a = 13/2

Length of latus rectum = 2b2/a = (2 × 32)/2 = (2×9)/2 = 18/2 = 9

4. 16x2 – 9y2 = 576

Solution:

Given:

The equation is 16x2 – 9y2 = 576

Let us divide the whole equation by 576, we get

16x2/576 – 9y2/576 = 576/576

x2/36 – y2/64 = 1

On comparing this equation with the standard equation of hyperbola y2/a2 – x2/b2 = 1,

We get a = 6 and b = 8,

It is known that, a2 + b2 = c2

So,

c2 = 36 + 64

c2 = 100

c = 10

Then,

The coordinates of the foci are (10, 0) and (-10, 0).

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

Eccentricity, e = c/a = 10/6 = 5/3

Length of latus rectum = 2b2/a = (2 × 82)/6 = (2×64)/6 = 64/3

5. 5y2 – 9x2 = 36

Solution:

Given:

The equation is 5y2 – 9x2 = 36

Let us divide the whole equation by 36, we get

5y2/36 – 9x2/36 = 36/36

y2/(36/5) – x2/4 = 1

On comparing this equation with the standard equation of hyperbola y2/a2 – x2/b2 = 1,

We get a = 6/5 and b = 2,

It is known that, a2 + b2 = c2

So,

c2 = 36/5 + 4

c2 = 56/5

c = (56/5)

= 214/5

Then,

The coordinates of the foci are (0, 214/5) and (0, – 214/5).

The coordinates of the vertices are (0, 6/5) and (0, -6/5).

Eccentricity, e = c/a = (214/5) / (6/5) = 14/3

Length of latus rectum = 2b2/a = (2 × 22)/6/√5 = (2×4)/6/5 = 45/3

6. 49y2 – 16x2 = 784.

Solution:

Given:

The equation is 49y2 – 16x2 = 784.

Let us divide the whole equation by 784, we get

49y2/784 – 16x2/784 = 784/784

y2/16 – x2/49 = 1

On comparing this equation with the standard equation of hyperbola y2/a2 – x2/b2 = 1,

We get a = 4 and b = 7,

It is know that, a2 + b2 = c2

So,

c2 = 16 + 49

c2 = 65

c = 65

Then,

The coordinates of the foci are (0, 65) and (0, –65).

The coordinates of the vertices are (0, 4) and (0, -4).

Eccentricity, e = c/a = 65/4

Length of latus rectum = 2b2/a = (2 × 72)/4 = (2×49)/4 = 49/2

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

7. Vertices (±2, 0), foci (±3, 0)

Solution:

Given:

Vertices (±2, 0) and foci (±3, 0)

Here, the vertices are on the x-axis.

So, the equation of the hyperbola is of the form x2/a2 – y2/b2 = 1

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

Since, the foci are (±3, 0), so, c = 3

It is know that, a2 + b2 = c2

So, 22 + b2 = 32

b2 = 9 – 4 = 5

∴ The equation of the hyperbola is x2/4 – y2/5 = 1

8. Vertices (0, ± 5), foci (0, ± 8)

Solution:

Given:

Vertices (0, ± 5) and foci (0, ± 8)

Here, the vertices are on the y-axis.

So, the equation of the hyperbola is of the form y2/a2 – x2/b2 = 1

Since, the vertices are (0, ±5), so, a = 5

Since, the foci are (0, ±8), so, c = 8

It is know that, a2 + b2 = c2

So, 52 + b2 = 82

b2 = 64 – 25 = 39

∴ The equation of the hyperbola is y2/25 – x2/39 = 1

9. Vertices (0, ± 3), foci (0, ± 5)

Solution:

Given:

Vertices (0, ± 3) and foci (0, ± 5)

Here, the vertices are on the y-axis.

So, the equation of the hyperbola is of the form y2/a2 – x2/b2 = 1

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

Since, the foci are (0, ±5), so, c = 5

It is known that, a2 + b2 = c2

So, 32 + b2 = 52

b2 = 25 – 9 = 16

∴ The equation of the hyperbola is y2/9 – x2/16 = 1

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

Solution:

Given:

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

Here, the foci are on x-axis.

The equation of the hyperbola is of the form x2/a2 – y2/b2 = 1

Since, the foci are (±5, 0), so, c = 5

Since, the length of the transverse axis is 8,

2a = 8

a = 8/2

= 4

It is known that, a2 + b2 = c2

42 + b2 = 52

b2 = 25 – 16

= 9

∴ The equation of the hyperbola is x2/16 – y2/9 = 1

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

Solution:

Given:

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

Here, the foci are on y-axis.

The equation of the hyperbola is of the form y2/a2 – x2/b2 = 1

Since, the foci are (0, ±13), so, c = 13

Since, the length of the conjugate axis is 24,

2b = 24

b = 24/2

= 12

It is known that, a2 + b2 = c2

a2 + 122 = 132

a2 = 169 – 144

= 25

∴ The equation of the hyperbola is y2/25 – x2/144 = 1

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

Solution:

Given:

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

Here, the foci are on x-axis.

The equation of the hyperbola is of the form x2/a2 – y2/b2 = 1

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

Length of latus rectum is 8

2b2/a = 8

2b2 = 8a

b2 = 8a/2

= 4a

It is known that, a2 + b2 = c2

a2 + 4a = 45

a2 + 4a – 45 = 0

a2 + 9a – 5a – 45 = 0

(a + 9) (a -5) = 0

a = -9 or 5

Since, a is non – negative, a = 5

So, b2 = 4a

= 4 × 5

= 20

∴ The equation of the hyperbola is x2/25 – y2/20 = 1

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

Solution:

Given:

Foci (± 4, 0) and the latus rectum is of length 12

Here, the foci are on x-axis.

The equation of the hyperbola is of the form x2/a2 – y2/b2 = 1

Since, the foci are (± 4, 0), so, c = 4

Length of latus rectum is 12

2b2/a = 12

2b2 = 12a

b2 = 12a/2

= 6a

It is known that, a2 + b2 = c2

a2 + 6a = 16

a2 + 6a – 16 = 0

a2 + 8a – 2a – 16 = 0

(a + 8) (a – 2) = 0

a = -8 or 2

Since, a is non – negative, a = 2

So, b2 = 6a

= 6 × 2

= 12

∴ The equation of the hyperbola is x2/4 – y2/12 = 1

14. Vertices (±7, 0), e = 4/3

Solution:

Given:

Vertices (±7, 0) and e = 4/3

Here, the vertices are on the x- axis

The equation of the hyperbola is of the form x2/a2 – y2/b2 = 1

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

It is given that e = 4/3

c/a = 4/3

3c = 4a

Substitute the value of a, we get

3c = 4(7)

c = 28/3

It is known that, a2 + b2 = c2

72 + b2 = (28/3)2

b2 = 784/9 – 49

= (784 – 441)/9

= 343/9

∴ The equation of the hyperbola is x2/49 – 9y2/343 = 1

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

Solution:

Given:

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

Here, the foci are on y-axis.

The equation of the hyperbola is of the form y2/a2 – x2/b2 = 1

Since, the foci are (±√10, 0), so, c = √10

It is known that, a2 + b2 = c2

b2 = 10 – a2 ………….. (1)

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

So, 9/a2 – 4/b2 = 1 … (2)

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

9/a2 – 4/(10-a2)2 = 1

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

So, a2 = 5

b2 = 10 – a2

= 10 – 5

= 5

∴ The equation of the hyperbola is y2/5 – x2/5 = 1


Access Other Exercise Solutions of Class 11 Maths Chapter 11- Conic Sections

Exercise 11.1 Solutions 15 Questions

Exercise 11.2 Solutions 12 Questions

Exercise 11.3 Solutions 20 Questions

Miscellaneous Exercise On Chapter 11 Solutions 8 Questions

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