First of all, you should know that the square of 12 144 plus the square of 5/25 equals the square of 13 169. According to Pythagorean theorem, this triangle is a right triangle. Then take ABC as three vertices, O as the center of the inscribed circle, and three sides passing through O as vertical lines respectively. The vertical foot (EFG: E on AB, F on BC, G on AC) is the tangent point of the circle and the edge, and the length from the center of the circle to the vertical foot is the radius. Since the center of the inscribed circle is the intersection point of the bisector of the inner angle, it is easy to see that AE is equal to AG (set as X), be is equal to BF (set as Y) and CF is equal to CG (set as Z). Knowing the length of three sides can solve a ternary linear equation group. Mainly for. Finally, BEOF is a square. The radius is twice the square root of BE. You'd better draw a picture!