For Problems 59–62, the lines that bisect each angle of a triangle meet in a single point O, and the perpendicular distance r from O to each side of the triangle is the same. The circle with center at O and radius r is called the inscribed circle of the triangle (see the figure).

Use the result of Problem 59 and the results of Problems 62 and 63 in Section 7.3 to show that

where s = 1/2(a + b + c ).

P b R 0 C n a enla Q