Question

sin(x+π/8)sin(x-π/8)​

Answer 1

1/2*[cos(x+π/8-x+π/8)-cos(x+π/8+x-π/8)]=1/2*(cosπ/4-cos2x)=

=1/2*√2/2-1/2*cos2x=√2/4-1/2*cos2x