a) 180°-120°=60°
90°+60°=150°
180°-150°=30°
[tex]\alpha[/tex] = 30°
b) 180°-100°=80°
180°-80°=100°
100°:2=50°
[tex]\alpha[/tex] = 50°
c) 180°-100°=80°
180°-80°-50°=50°
180°-50°=130°
[tex]\alpha[/tex] = 130°
