Răspuns:
Explicație pas cu pas:
a + b + c + d = 360°
a + c = 2b
b + d = 2c
b = 4c/5
a + c + 2c = 360°
a + 3c = 360°
a + c = 8c/5
a = 8c/5 - c = 8c/5 - 5c/5 = 3c/5
3c/5 + 3c = 360°
3c/5 + 15c/5 = 360°
18c/5 = 360°
c = 5*360°/18 = 100°
a = 3*100°/5 = 60°
b = 4*100°/5 = 80°
d = 2*100° - 80° = 200° - 80° = 120°