Cos105градусов *sin105градусов

Question

Cos105градусов *sin105градусов

Answer 1

Cos105°*sin105°=(1/2)sin(105°*2)=(1/2)sin210°=
=(1/2)sin(270°-60°)=(1/2)(sin270°cos60°-cos270°sin60°)=
=(1/2)(-1*(1/2) -0*(√3/2)) = (1/2)*(-1/2)=-1/4