NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 36
Total: 71
4x2+9y2 = 36
Solution:  
Given equation of ellipse is 4x2+9y2 = 36
i.e.,
4x2
9y2
36
= 1 ⇒
x2
9
+
y2
4
= 1
Clearly, 9 > 4 ⇒ a2 = 9 and b2 = 4
The equation of ellipse in standard form is
x2
a2
+
y2
b2
= 1
∴ a2 = 9 ⇒ a = 3 and b2 = 4 ⇒ b = 2
We know that c = √a2−b2 ⇒ c = √9−4 = √5
∴ Coordinates of foci are (±c, 0) i.e. (± √5, 0)
Coordinates of vertices are (±a, 0) i.e. (±3, 0).
Length of major axis = 2a = 2 × 3 = 6
Length of minor axis = 2b = 2 × 2 = 4
Eccentricity (e) =
c
a
=
√5
3

Length of latus rectum =
2b2
a
=
2×4
3
=
8
3
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