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10-2. Parabola, Ellipse, Hyperbola
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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