AB=AC. }
}=> m(B)=m(C)=(180°-120°):2=60°:2=30°
m(A)=120°. }
∆OAB-dreptunghic: m(AOB)=90°
m(B)=30°
=>AO=AB/2=4/2=2 (cm)
din teorema lui Pitagora => OB²+OA²=AB²
OB²+2²=4²
OB²+4=16
OB²=12
OB =2√3(cm)
raza= OB=2√3 cm
