Q.

If the normals of the parabola y2=4x drawn at the end points of its latus rectum are tangents to the circle x-32+y+22=r2, then the value of r2 is

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a

2

b

8

c

1

d

4

answer is B.

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Detailed Solution

Given y2=4x    a=1  Now  L=(a,2a)=(1,2) Equation  of the normal at L is y-y1=-y12a(x-x1) y-2=-22(x-1) y-2=-x+1 x+y-3=0

it is tangent of the circle

 (x-3)2+(y+2)2=r2  with centre(C)=(3,-2) then r=d   r=3-2-32=2 r2=2

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