1 1, and the theorem n is equal to: (n-2) * 180, then the degree of each internal angle of a regular polygon is: (n-2) *180 ÷ n. So: (n-2) *. Then its side length is: 63 divided by 7=9.

12, (2n-2) * 180 = 2 160, that is, n=7 is the number of primary edges.

13, angle BCD=60, angle BCD = 120, angle BCM=60, angle BCN=30, so angle DCN=30.