Parabola 2 Question 33

12. The equation of the common tangent to the curves y2=8x and xy=1 is

(2002, 1M)

(a) 3y=9x+2

(b) y=2x+1

(c) 2y=x+8

(d) y=x+2

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Solution:

  1. Tangent to the curve y2=8x is y=mx+2m. So, it must satisfy xy=1

xmx+2m=1mx2+2mx+1=0

Since, it has equal roots.

D=04m24m=0m3=1m=1

Hence, equation of common tangent is y=x+2.



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