Помогите упростить sin(a-3/2П)cos(300+a)-cos(60-2a).

= - sin(3π/2-α)·cos(360-60-α)-cos(60-2α)=cosα·cos(60+α)-cos(60-2α)==0.5·( cos(α-60-α)+cos(α+60+α) )-cos(60-2α) =0.5·( 0.5+cos(60+2α))-cos (60-2α) =0.25 +0.5·(cos 60·cos2α-sin60·sin2α) -  cos60·cos2α+sin60·sin2α ==0.25 +0.25·cos2α-√3/4·sin2α-0.5cos2α+√3/2·sin2α =0.25-0.25cos2α+√3/4·sin2α