11-a=20°(BIC tr. isoscel, I=100 rezulta in tr. BIC unghiul IBC/ICB=40 =>B/C=80=>A=20)
12-x+y=180(doua unghiuri consecutive intr-un traoez formeaza adunate 180°)
13-BAC=60°(BAC echilateral,jumatate din rombul OBAC)
14-tr.ABC=tr. dreptunghic=>u.ABC=30°
15-tr.echilateral=>x=60°
