NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 28
Total: 71
x2
36
+
y2
16
= 1
Solution:  
We have been given an equation of ellipse
x2
36
+
y2
16
= 1
Clearly, 36 > 16
The equation of ellipse in standard form is
x2
a2
+
y2
b2
= 1
∴ a2 = 36 ⇒ a = 6 and b2 = 16 ⇒ b = 4
We know that
c = √a2−b2 ⇒ c = √36−16 = √20
∴ Coordinates of foci are (±c, 0) i.e. (± √20, 0)
Coordinates of vertices are (± a, 0) i.e. (± 6, 0).
Length of major axis = 2a = 2 × 6 = 12
Length of minor axis = 2b = 2 × 4 = 8
Eccentricity (e) =
c
a
=
√20
6

Length of latus rectum =
2b2
a
=
2×16
6
=
16
3
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