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NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 53 of 71
Marks: +1, -0
49y216x249y^2 - 16x^2 = 784
Solution:  
Given equation of hyperbola is 49y216x249y^2 - 16x^2 = 784
i.e., 49y278416x2784\frac{49y^2}{784} - \frac{16x^2}{784} = 1 ⇒ y216x249\frac{y^2}{16} - \frac{x^2}{49} = 1
which is of the form y2a2x2b2\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1.
The foci and vertices of the hyperbola lie on y-axis.
Now, a2a^2 = 16 ⇒ a = 4 and b2b^2 = 49 ⇒ b = 7
Also, c2c^2 = a2+b2a^2 + b^2 = 16 + 49 = 65 ⇒ c = 65
∴ Coordinates of foci are (0, ±c) i.e. (0,±64)(0, \pm \sqrt{64})
Coordinates of vertices are (0, ±a) i.e. (0, ±4)
Eccentricity (e) = ca\frac{c}{a} = 654\frac{\sqrt{65}}{4}
Length of latus rectum = 2b2a\frac{2b^2}{a} = 2×494\frac{2 \times 49}{4} = 492\frac{49}{2}.
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