NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 50
Total: 71
9y24x2 = 36
Solution:  
Given equation of hyperbola is 9y24x2 = 36
i.e.,
9y2
36
4x2
36
= 1 ⇒
y2
4
x2
9
= 1 , which is of the form
y2
a2
x2
b2
= 1.
The foci and vertices of the hyperbola lie on y-axis.
Now, a2 = 4 ⇒ a = 2 and b2 = 9 ⇒ b = 3
Also, c2 = a2+b2 = 4 + 9 = 13 ⇒ c = 13
∴ Coordinates of foci are (0, ± c) i.e. (0, ± 13)
∴ Coordinates of vertices are (0, ±a) i.e. (0, ±2)
Eccentricity (e) =
c
a
=
13
2

Length of latus rectum =
2b2
a
=
2×9
2
= 9.
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