по теореме косинусов:
с^2=a^2+b^2-2a*b*cos 120
c^2=8*8+3√3*3√3-2*8*3√3*(-1/2)=64+27+24√3=91+24√3
с= √(91+24√3)
по теореме косинусов:
с^2=a^2+b^2-2a*b*cos 120
c^2=8*8+3√3*3√3-2*8*3√3*(-1/2)=64+27+24√3=91+24√3
с= √(91+24√3)