Sin5П/8*Sin7П/8*Sin7П/4

Question

Sin5П/8*Sin7П/8*Sin7П/4

Answer 1

1/2(сos(7π/8-5π/8)-cos(7π/8+5π/8))sin(2π-π/4)=1/2(cosπ/4-cos3π/2)*sin(-π/4)=
=1/2(√2/2-0)*(-√2/2)=-1/2*(√2/2)²=-1/2*1/2=-1/4