cos(45+30)cos(45-30)+sin(45+30)sin(45-30=)

问题描述:

cos(45+30)cos(45-30)+sin(45+30)sin(45-30=)

cos(45+30)cos(45-30)+sin(45+30)sin(45-30)
=cos[(45+30)-(45-30)]
=cos(75-15)
=cos60
=1/2