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0. Make a sketch to follow my arguments.
Let O be the center of the circle located on the leg AB, and
P be the tangent point lying on the hypotenuse AC.
1. Two right-angled triangles are similar: triangle ABC and triangle APO.
2. Regarding the triangle ABC, notice that its sides are 5 (the leg AB), (the hypotenuse AC) and = = 6 (the other leg BC).
3. Let r be the unknown radius of the circle.
4. Use two proportions that follow the similarity of the triangles:
= ,
which after substituting the data takes the form
= .
From this point, can you complete the solution on your own ?
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