urgent, grabitiva dau coroana

a) ∠ACB=180-120
∠ACB=60
b) ΔABC=180
ΔABC=∠A+∠B+∠C=180
∠A=∠B
=>∠A+∠B+60=180
=> ∠A+∠B=180-60
=> ∠A+∠B=120
=> 120:2=60
∠BAC=60
∠ABC=60
=> ΔABC este echilateral