2. A polygon with equal sides and angles is a regular polygon. Let the number of sides of one polygon be x and the number of sides of another polygon be 2x. The sum of the interior angles of a polygon is (n-2) x180 (x-2) x180/x divided by (2x-2) x180/2x = 3/4x = 52x = 65438.
3.(n-20)x 180 = 2570n = 130D
When 4N+N*(N-3)/2 is less than 20, the number divisible by 5 is 5, 15, 10, and n is d.