TITLE: radius of circle inscribed in rectangle
QUESTION [5 upvotes]: I have two circles inside a rectangle(4 * 6), where the diameter of one of both is the total length of a side of the rectangle, and the other circle diameter is part of the length of the another side.
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What is the name of the theory behind this problem?
How to find the radius R?

REPLY [3 votes]: Hint: note the right triangle below.  What does this tell you about $R$?