Engineering Board Exam Reviewer · Circles · medium

Two circles are externally tangent. The centers are (0,0) and (12,5), and the first circle has radius 4. Find the radius of the second circle.

1. 17
2. 13
3. 4.5
4. 9

Answer

D. 9

Solution

The distance between centers is sqrt(122+52)=13=r1+r2, so r2=13-4=9.

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