cos6 cos54-sin6 sin 54

Question

cos6 cos54-sin6 sin 54

Answer 1

=cos54cos6-sin54sin6= по формулам coscos и sin sin
(1/2)[cos(54-6)+cos(54+6)]-1/2[cos(54-6)-cos(54+6)]=
cos(54+6)=cos60° =1/2