The radius of the inscribed circle of a right triangle r=(a+b-c)/2, where a and b are the lengths of the right side and c is the length of the hypotenuse.

General triangle: r=2S/(a+b+c), where s is the area of the triangle and a, b and c are the three sides of the triangle. In addition, under the radical sign, S= p(p-a)(p-b)(p-c), where p=(a+b+c)/2.