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10-2. Parabola, Ellipse, Hyperbola
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If the circle $x^2 + y^2 = a^2$ intersects the hyperbola $xy = c^2 $ in four points $ P(x_1, y_1), Q(x_2, y_2), R(x_3, y_3), S(x_4, y_4), $ then
A
$x_1 + x_2 + x_3 + x_4 = 0$
B
$y_1 + y_2 + y_3 + y_4 = 0$
C
$x_1 x_2 x_3 x_4 = c^4$
D
all of the above
Solution
solving $xy = c^2$ and $x^2 + y^2 = a^2$
$x^2 +\frac{{{c^4}}}{{{x^2}}}\, = a^2$
$x^4- ax^3- a^2x^2 + ax + c^4 = 0$
$\Rightarrow$ ${\sum x _i}\, = \,0$;${\sum y _i}\, = \,0$
$x_1 x_2 x_3 x_4 = c^4$ $\Rightarrow$ $y_1 y_2 y_3 y_4 = c^4$
Standard 11
Mathematics