2(√3/2*sinπ/12+1/2*cosπ/12)=2(sinπ/12cosπ/6+cosπ/12sinπ/6)=
=2sin(π/12+π/6)=2sinπ/4=2*√2/2=√2
(cosα-cosβ)·(cosα+cosβ) =cos²a-cos²b
-sin(α-β)sin(α+β)=-1/2*(cos(a-b-a-b)-cos(a-b+a+b))=
=-1/2*(cos2b-cos2a)=-1/2(2cos²b-1)+1/2(2cos²a-1)=
=-cos²b+1/2+cos²a-1/2=cos²a-cos²b
cos²a-cos²b=cos²a-cos²b