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

Circles are drawn on chords of the rectangular hyperbola $ xy = c^2$  parallel to the line $ y = x $ as diameters. All such circles pass through two fixed points whose co-ordinates are :

A

$(c, c)$

B

$(- c, - c)$

C

$(- c, c)$

D

both $(A)$ and $(B)$

Solution

$1/(t_1t_2) = – 1; $ $(x – ct_1) (x -ct_2) $+$\left( {y\,\, – \,\,{\textstyle{c \over {{t_1}}}}} \right)$$\left( {y\,\, – \,\,{\textstyle{c \over {{t_2}}}}} \right)$ $ = 1$
use $t_1t_2 = – 1 $ gives
$(x^2 + y^2 – 2c^2) – (t_1 + t_2) (x – y) = 0 $ $\Rightarrow $ $S + \lambda L = 0 $ 

Standard 11
Mathematics

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