We are given the equation \( (a - b)(s - c) = (b - c)(s - a) \), and we need to determine the type of progression for \( r_1, r_2, r_3 \).
Step 1: The given condition leads to an important identity related to the sides and the semiperimeter of the triangle. This implies that the values \( r_1, r_2, r_3 \) are related in a way that they form an arithmetic progression.
Thus, \( r_1, r_2, r_3 \) are in an arithmetic progression.