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Question: Answered & Verified by Expert
If a circle of radius R passes through the origin O and intersects the coordinate axes at A and B, then the locus of the foot of perpendicular from O on AB is :
MathematicsCircleJEE MainJEE Main 2019 (12 Jan Shift 2)
Options:
  • A x2+y2x+y=R2xy
  • B x2+y23=4R2x2y2
  • C x2+y22=4R2x2y2
  • D x2+y22=4Rx2y2
Solution:
1676 Upvotes Verified Answer
The correct answer is: x2+y23=4R2x2y2

Since, circle passing through origin intersect the coordinate axes at A& B, hence AB must be diameter and AB=2R.

Now, let foot of the perpendicular from origin upon AB be Ph, k.

Slope of line OP=k-0h-0=kh

Since, line ABOP slope of AB=-hk

Thus, equation of line  AB is y-k=-hkx-h

For co-ordinates of A, put y=00-k=-hkx-hx=h2+k2hA h2+k2h, 0.

For co-ordinates of B, put x=0y-k=-hk0-hy=h2+k2kB 0,h2+k2k.

Now, given AB=2R

Applying distance formula,

h2+k2h-02+0-h2+k2k2=2R

h2+k22 1h2+1k2=4R2h2+k23=4R2h2k2

Hence, locus is x2+y23=4R2x2y2

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