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AB is the diameter of the semicircle with center O. Circles P and Q are tangent to each other and to the semicircle. If OB=4, find the radius of circle Q.

I haven't been able to make any headway at all with this problem. I tried to find a system of equations with the radius of circle Q equal to x and some other length equal to y, but all I found was that the length of the common external tangent of circles P and Q is [tex] 2 \sqrt{2x} [/tex], where x is the radius of circle Q, and I'm not sure how that's useful. Please help.

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# Homework Help: Need Help With Geometry Problem (Circles)

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