S= (n-2) • 180 grade; n-numărul de laturi
(5-2)•180= 540 grade
540:5= 108 grade are un unghi al unui pentagon regulat.
(6-2)•180=720 grade
720:6= 120 grade are un unghi al unui Hexagon regulat.
(8-2)•120=1080 grade
1080:6=180 grade are un unghi al unui octogon regulat