# Four Visual Proofs of a Theorem about a Regular Nonagon

Four Visual Proofs of a Theorem about a Regular Nonagon

This Demonstration shows four visual proofs that , where , , and are the lengths of a side, the shortest diagonal, and the longest diagonal, respectively, of a regular nonagon. The interior angle of the regular nonagon is , so that angle 451 equals .

a+d=D

a

d

D

°

160

°

60