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NCERT Class XI Mathematics - Conic Sections - Solutions

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Question : 57 of 71
Marks: +1, -0
Foci (±5, 0), the transverse axis is of length 8.
Solution:  
Here foci are (±5, 0) which lie on x-axis.
So the equation of the hyperbola in standard form is x2a2y2b2\frac{x^2}{a^2}-\frac{y^2}{b^2} = 1.
Now, Foci are (±5, 0) ⇒ ae = 5, Length of transverse axis, 2a = 8 ⇒ a = 4
Now, ae = 5 ⇒ e = 5a\frac{5}{a} ⇒ e = 54\frac{5}{4}
We know that b = ae21a\sqrt{e^2-1} ⇒ b = 4251614\sqrt{\frac{25}{16}-1} = 4 × 34\frac{3}{4} = 3
Thus required equation of hyperbola is x242y232\frac{x^2}{4^2}-\frac{y^2}{3^2} = 1 ⇒ x216y29\frac{x^2}{16}-\frac{y^2}{9} = 1.
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