[tex]\it a)\ \ BC=diametrul\ cercului \Rightarrow BC=2\cdot R=2\cdot2=4\ cm\\ \\ b)\ OA=OB\ (raze) \Rightarrow \Delta OAB-isoscel\ \ \c{s}i\ m(\widehat{BAO})=60^o\Rightarrow \\ \\ \Rightarrow \Delta OAB-echilateral \Rightarrow m(\hat B)=60^o \\ \\ m(\stackrel\frown{CA})=2\cdot m(\hat B)=2\cdot60^o=120^o[/tex]
