[질문] 삼각형에서a=3,b=4,C=120°일때c와넓이S는??

두변:a,b,끼인각:C일때,c^2=a^2+b^2-2ab*cosC라는관계가성립하므로,c^2=9+16-2*3*4*cos120°=25-24*(-0.5)=37이므로c=√37,넓이S=absin120°=3*4*√3/2=6√3이에요