Possible Duplicate:
Triangle and Incircle
In a setup of right triangles ABC, BDA, and BDC not unlike this
(click on the link, and ignore the written side measures and subtext in that diagram- we don't know any side-lengths here)
The incircle(inscribed circle) of triangle BDA has radius=5 and the incircle of BDC has radius=3. What is the radius of the incircle of ABC?