Sin 3п/4 sin 7п/4 cos 3п/4 cos 7п/4

Question

Sin 3п/4 sin 7п/4 cos 3п/4 cos 7п/4

Answer 1

1/2sin3π/2*1/2sin7π/2=1/4*(-1)*sin(4π-π/2)=-1/4*(-sinπ/2)=-1/4*(-1)=1/4