72. A simple closed polygon consists of n points in the plane joined in pairs by n line segments; each point is segments. Following are two examples. a. Use the first principle of induction to prove that the sum of the interior angles of an n-sided simple closed polygon is (n - 2)180 for all n 3 b. Use the second principle of induction to prove that the sum of the interior angles of an n-sided simple closed polygon is (n - 2)180 for all n 2 3