Prove that the tangent at any point to the rectangular hyperbola forms with the asymptotes, a triangle of constant area.
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Solution
The equation of tangent to xy=c2 at 't' is x+yt2=2ct When y=0; x=2ct ∴Q=(2ct,0) When x=0; y=2ctt2=2ct ∴R=(0,2ct) Now area of ΔOQR=12×2ct×2ct =2c2, which is a constant.