Dadas as expressões:

$$a_1=A\mathrm{sen}(x+\theta )$$

$$a_2=A\mathrm{sen}(x+2\pi /3+\theta )$$ 

$$a_3=A\mathrm{sen}(x-2\pi /3+\theta )$$

$$b_1=B\mathrm{sen}(x+\theta +\phi )$$

$$b_2=B\mathrm{sen}(x+2\pi /3+\theta +\phi )$$

$$b_3=B\mathrm{sen}(x-2\pi /3+\theta +\phi )$$

Calcule $C=a_1{b}_1+a_2{b}_2+a_3{b}_3$.