MCQ
The equation to the chord joining two points $(x_1, y_1)$  and $(x_2, y_2)$  on the rectangular hyperbola $xy = c^2$  is
  • $\frac{x}{{{x_{1\,}}\, + \,\,{x_2}}}$+$\frac{y}{{{y_{1\,}}\, + \,\,{y_2}}}$ $ = 1$ 
  • B
    $\frac{x}{{{x_{1\,}}\, - \,\,{x_2}}}$+$\frac{y}{{{y_{1\,}}\, - \,\,{y_2}}} = 1$
  • C
    $\frac{x}{{{y_{1\,}}\, + \,\,{y_2}}}$+$\frac{y}{{{x_{1\,}}\, + \,\,{x_2}}} = 1$
  • D
    $\frac{x}{{{y_{1\,}}\, - \,\,{y_2}}}$+$\frac{y}{{{x_{1\,}}\, - \,\,{x_2}}}= 1$

Answer

Correct option: A.
$\frac{x}{{{x_{1\,}}\, + \,\,{x_2}}}$+$\frac{y}{{{y_{1\,}}\, + \,\,{y_2}}}$ $ = 1$ 
a
note that chord of $ xy = c^2$  whose middle point is $(h, k)$  in $\frac{x}{h}\, + \,\frac{y}{k}\, = \,2$ further, now $2h = x_1 + x_2 $ and $2k = y_1 + y_2$

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