Engineering
Mathematics
Tangent of Parabola
Question

The common tangents to the circle x2 + y2 = 2 and the parabola y2 = 8x touch the circle at the points P, Q and the parabola at the points R, S. Then the area of the quadrilateral PQRS is :

3

15

6

9

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Solution

Tangent to y2 = 8x is y = mx + 2m also touches x2 + y2 = 2

        |2m1+m2|  =  2

         m = ± 1

Tangent:  y = x + 2 and y = – x – 2

         point of intersection of tangents (–2, 0)  foot of directrix

Area = 2 (12(1+4)×3) = 15