Răspuns:
12. a+2a = 90° (complement)
3a = 90°
a = 90 : 3 = 30°
2a = 30 ° × 2 = 60°
13. a+8a= 180°
9a = 180°
a = 180° : 9 = 20
8a = 8•20 = 160°
