Cosп/12*cos7п/12-sinп/12*sin7п/12

Question

Cosп/12*cos7п/12-sinп/12*sin7п/12

Answer 1

Cos(п/12)*cos(7п/12)-sin(п/12)*sin(7п/12)=cos((п/12)+(7п/12))=cos(3п/4)=-√(2)/2.