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NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 34 of 71
Marks: +1, -0
36x2+4y236x^2 + 4y^2 = 144
Solution:  
Given equation of ellipse is 36x2+4y236x^2 + 4y^2 = 144
i.e., 36x2144+4y2144\frac{36x^2}{144} + \frac{4y^2}{144} = 1 ⇒ x24+y236\frac{x^2}{4} + \frac{y^2}{36} = 1
Clearly, 36 > 4
The equation of ellipse in standard form is y2a2+x2b2\frac{y^2}{a^2} + \frac{x^2}{b^2} = 1
a2a^2 = 36 ⇒ a = 6 and b2b^2 = 4 ⇒ b = 2
We know that c = a2b2\sqrt{a^2-b^2} ⇒ c = 364\sqrt{36-4} = 32\sqrt{32} = 424\sqrt{2}
∴ Coordinates of foci are (0, ± c)
i.e. (0, ± 4 2\sqrt{2})
Coordinates of vertices are (0, ± a) i.e. (0, ± 6).
Length of major axis = 2a = 2 × 6 = 12
Length of minor axis = 2b = 2 × 2 = 4
Eccentricity (e) = ca\frac{c}{a} = 426\frac{4\sqrt{2}}{6} = 223\frac{2\sqrt{2}}{3}
Length of latus rectum = 2b2a\frac{2b^2}{a} = 2×46\frac{2\times 4}{6} = 43\frac{4}{3}
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