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10-2. Parabola, Ellipse, Hyperbola
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If $ P(x_1, y_1), Q(x_2, y_2), R(x_3, y_3) $ and $ S(x_4, y_4) $ are $4 $ concyclic points on the rectangular hyperbola $x y = c^2$ , the co-ordinates of the orthocentre of the triangle $ PQR$ are :
A
$(x_4, - y_4)$
B
$(x_4, y_4)$
C
$(- x_4, - y_4)$
D
$(- x_4, y_4)$
Solution
A rectangular hyperbola circumscribing a $ \Delta$ also passes through its orthocentre if $\left( {c{t_i},\,\frac{c}{{{t_i}}}} \right)$ where $i = 1, 2, 3 $ are the vertices of the $ \Delta $ then therefore orthocentre is $\left( {\frac{{ – c}}{{{t_1}{t_2}{t_3}}}, – c{t_1}{t_2}{t_3}} \right)$ , where $t_1 t_2 t_3 t_4 = 1.$ Hence orthocentre is $\left( { – c{t_4},\,\,\frac{{ – c}}{{{t_4}}}} \right)$ = $(- x_4 , – y_4)$
Standard 11
Mathematics