Maharashtra State Board 11th Maths Solutions Chapter 7 Conic Sections Ex 7.3

(ii) Given equation of the hyperbola is
Comparing this equation with , we get
b2= 16 and a2= 25
⇒ b = 4 and a = 5
Length of transverse axis = 2b = 2(4) = 8
Length of conjugate axis = 2a = 2(5) = 10
Co-ordinates of vertices are B(0, b) and B’ (0, -b)
i.e., B(0, 4) and B'(0, -4)
We know that

(iii) Given equation of the hyperbola is 16x2– 9y2= 144.
Comparing this equation with , we get
a2= 9 and b2= 16
⇒ a = 3 and b = 4
Length of transverse axis = 2a = 2(3) = 6
Length of conjugate axis = 2b = 2(4) = 8
We know that
e =
Co-ordinates of foci are S(ae, 0) and S'(-ae, 0),
i.e., S(3(), 0) and S'(-3(), 0)
i.e., S(5, 0) and S'(-5, 0)
Equations of the directrices are x = ±
=
=
Length of latus rectum =
(iv) Given equation of the hyperbola is 21x2– 4y2= 84.
Comparing this equation with , we get
a2= 4 and b2= 21
⇒ a = 2 and b = √21
Length of transverse axis = 2a = 2(2) = 4
Length of conjugate axis = 2b = 2√21
We know that

(v) Given equation of the hyperbola is 3x2– y2= 4.
Comparing this equation with , we get
a2= and b2= 4

(vi) Given equation of the hyperbola is x2– y2= 16.
Comparing this equation with , we get
a2= 16 and b2= 16
⇒ a = 4 and b = 4
Length of transverse axis = 2a = 2(4) = 8
Length of conjugate axis = 2b = 2(4) = 8
We know that
e =
Co-ordinates of foci are S(ae, 0) and S'(-ae, 0),
i.e., S (4√2, 0) and S’ (-4√2, 0)
Equations of the directrices are x = ±
⇒ x =
⇒ x = ± 2√2
Length of latus rectum = = 8
(vii) Given equation of the hyperbola is .
Comparing this equation with , we get
b2= 25 and a2= 9
⇒ b = 5 and a = 3
Length of transverse axis = 2b = 2(5) = 10
Length of conjugate axis = 2a = 2(3) = 6
Co-ordinates of vertices are B(0, b) and B’ (0, -b),
i.e., B(0, 5) and B’ (0, -5)
We know that

(viii) Given equation of the hyperbola is .
Comparing this equation with , we get
b2= 25 and a2= 144
⇒ b = 5 and a = 12
Length of transverse axis = 2b = 2(5) = 10
Length of conjugate axis = 2a = 2(12) = 24
Co-ordinates of vertices are B(0, b) and B’ (0, -b),
i.e., B(0, 5) and B’ (0, -5)
We know that

(ix) Given equation of the hyperbola is
Comparing this equation with , we get
a2= 100 and b2= 25
⇒ a = 10 and b = 5
Length of transverse axis = 2a = 2(10) = 20
Length of conjugate axis = 2b = 2(5) = 10
We know that

(x) Given equation of the hyperbola is x = 2 sec θ, y = 2√3 tan θ.
Since sec2θ – tan2θ = 1,
Comparing this equation with , we get
a2= 4 and b2= 12
⇒ a = 2 and b = 2√3
Length of transverse axis = 2a = 2(2) = 4
Length of conjugate axis = 2b = 2(2√3) = 4√3
We know that
e = = = 2
Co-ordinates of foci are S(ae, 0) and S'(-ae, 0),
i.e., S(2(2), 0) and S'(-2(2), 0),
i.e., S(4, 0) and S'(-4, 0)
Equations of the directrices are x = ±.
⇒ x = ±
⇒ x = ±1
Length of latus rectum = = 12



(ii) Let the required equation of hyperbola be
Length of conjugate axis = 2b
Given, length of conjugate axis = 6
⇒ 2b = 6
⇒ b = 3
⇒ b2= 9
Distance between foci = 2ae
Given, distance between foci = 10
⇒ 2ae = 10
⇒ ae = 5
⇒ a2e2= 25
Now, b2= a2(e2– 1)
⇒ b2= a2e2– a2
⇒ 9 = 25 – a2
⇒ a2= 25 – 9
⇒ a2= 16
The required equation of hyperbola is
(iii) Let the required equation of hyperbola be
Given, eccentricity (e) =
Distance between directrices =
Given, distance between directrices =


(iv) Let the required equation of hyperbola be
……(i)
Length of conjugate axis = 2b
Given, length of conjugate axis = 12
⇒ 2b = 12
⇒ b = 6 …..(ii)
⇒ b2= 36
The hyperbola passes through (1, -2)
Substituting x = 1 and y = -2 in (i), we get

(v) Let the required equation of hyperbola be
……(i)
The hyperbola passes through the points (6, 9) and (3, 0).

(vi) Let the required equation of hyperbola be
Co-ordinates of vertices are (±a, 0).
Given that, co-ordinates of vertices are (±7, 0)
∴ a = 7
Endpoints of the conjugate axis are (0, b) and (0, -b).
Given, the endpoints of the conjugate axis are (0, ±3).
∴ b = 3
The required equation of hyperbola is
i.e.,
(vii) Let the required equation of hyperbola be
……(i)
Given, eccentricity (e) =
Co-ordinates of foci are (±ae, 0).
Given co-ordinates of foci are (±2, 0)
ae = 2
⇒ a() = 2
⇒ a =
⇒ a2=
(viii) Let the required equation of hyperbola be
Length of transverse axis = 2a
Given, length of transverse axis = 6
⇒ 2a = 6
⇒ a = 3
⇒ a2= 9
Length of conjugate axis = 2b
Given, length of conjugate axis = 9
⇒ 2b = 9
⇒ b =
⇒ b2=
The required equation of hyperbola is
i.e.,
(ix) Let the required equation of hyperbola be
Length of transverse axis = 2a
Given, length of transverse axis = 8
⇒ 2a = 8
⇒ a = 4
⇒ a2= 16
Distance between foci = 2ae
Given, distance between foci = 10
⇒ 2ae = 10
⇒ ae = 5
⇒ a2e2= 25
Now, b2= a2(e2– 1)
⇒ b2= a2e2– a2
⇒ b2= 25 – 16 = 9
The required equation of hyperbola is









Alternate method:
Given equation of the hyperbola is
…….(i)
Given equation of the line is 3x – 4y = k
y =
Substituting this value ofy in (i), we get
⇒
⇒ 4x2– (9x2– 6kx + k2) = 20
⇒ 4x2– 9x2+ 6kx – k2= 20
⇒ -5x2+ 6kx – k2= 20
⇒ 5x2– 6kx + (k2+ 20) = 0 …..(ii)
Since, the given line touches the given hyperbola.
The quadratic equation (ii) in x has equal roots.
(-6k)2– 4(5)(k2+ 20) = 0
⇒ 36k2– 20k2– 400 = 0
⇒ 16k2= 400
⇒ k2= 25
⇒ k = ±5
