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A circle of radius 2 unit passes through the vertex and the focus of the parabola y2=2x and touches the parabola y=x-142+α, where α>0. Then 4α-82 is equal to ______.
MathematicsParabolaJEE MainJEE Main 2022 (27 Jun Shift 1)
Solution:
2862 Upvotes Verified Answer
The correct answer is: 63

The vertex and focus of parabola y2=2x are V0,0 and S12,0 respectively

Let the equation of circle passing through vertex and focus of the parabola be x-h2+y-k2=4

 Circle passes through 0,0

h2+k2=4     1

 Circle passes through 12,0

12-h2+k2=4

h2+k2=h+154     2

On solving 1 and 2

4=h+154

h=14

k=634

here k=-634 is rejected as circle with centre 14,-634 can't touch the parabola y2=2x.

So the equation of circle will be x-142+k-6342=4

Since this circle touches the parabola y=x-142+α

i.e. α=2+634=8+634

4α-8=63

4α-82=63

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