suma unghiurilor unui poligon convex = ( n - 2) ×180 ⁰
a) 1260⁰ = ( n - 2 ) ×180⁰ n - 2 = 1260⁰ :180 ⁰= 7 n = 9
b) 1800⁰ = ( n - 2 ) × 180⁰ n -2 =10 n = 12
c) 3240⁰ = ( n - 2 )×180 ⁰ n - 2 = 3240⁰ :180⁰=18 n = 20
d ) 2700⁰= ( n - 2 ) ×180⁰ n - 2 = 2700 ⁰:180⁰=15 n = 17