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Question: If the normal to the hyperbola xy = c<sup>2</sup> at the point t<sub>1</sub> meets the curve again a...

If the normal to the hyperbola xy = c2 at the point t1 meets the curve again at the point t2 then t1t2 equals.

A

-1

B

t12- t_{1}^{- 2}

C

1/t1

D

1

Answer

-1

Explanation

Solution

Normal at P (ct1, c/t1) is ct13yt1ct14+c=0c{t_{1}}^{3} - yt_{1} - c{t_{1}}^{4} + c = 0.

If it passes through Q (ct2, c/t2), then

ct2t13ct1t2ct14+c=0ct_{2}{t_{1}}^{3} - \frac{ct_{1}}{t_{2}} - c{t_{1}}^{4} + c = 0.

On simplification, we get t1t2 = -1.