Gujarati
Hindi
10-2. Parabola, Ellipse, Hyperbola
normal

With one focus of the hyperbola $\frac{{{x^2}}}{9}\,\, - \,\,\frac{{{y^2}}}{{16}}\,\, = \,\,1$ as the centre , a circle is drawn which is tangent to the hyperbola with no part of the circle being outside the hyperbola. The radius of the circle is

A

$less\ than$ $2$

B

$2$

C

$\frac{{11}}{3}$

D

$none$

Solution

$e^2 = 1 + \frac{{16}}{9}\,$ $= $  $\frac{{25}}{9}\,$

$\Rightarrow $ $e = \frac{5}{3}\,$
$\therefore$ focus $= (5, 0)$

Use reflection property to prove that circle cannot touch at two points.

It can only be tangent at the vertex $r = 5 – 3 = 2 $ 

Standard 11
Mathematics

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