14sin 7π/12 × cos 7π/12помогите решить

14sin 7π/12 × cos 7π/12=7*2sin 7π/12*cos 7π/12=7sin(2*7π/12)=7sin 7π/6=7sin(π+π/6)=-7sin π/6=-7*1/2=-7/2=-3,5.