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Question: Answered & Verified by Expert
Let C1 and C2 be two circles of radius r1 and r2 respectively r1>r2 touching both the axes. If the two circles are orthogonal, then r1r2 is equal to
MathematicsCircleJEE Main
Options:
  • A 2
  • B 2+3
  • C 3+2
  • D 3
Solution:
2290 Upvotes Verified Answer
The correct answer is: 2+3
Let the equation of a circle touching both the axes be
x-r2+y-r2=r2
x2+y2-2rx-2ry+r2=0
If the two given circles are orthogonal, then 
2-r1-r2+2-r1-r2=r12+r22
r12-4r1r2+r22=0
r1r2=2+3

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