Question

помогите решить тригонометрию

Answer 1

sin15π/8=sin(16π-π/8)=sin(16π/8-π/8)=sin(2π-π/8)=-sinπ/8
cos15π/8=cos(2π-π/8)=cosπ/8
7×√2×(-sinπ/8)cosπ/8=-7×√2sinπ/8cosπ/8=-7×√2×2/2×sinπ/8cosπ/8=-7×√2/2×sin2π/8=-7×√2/2×sinπ/4=-7×√2/2×√2/2=-7/2=-3,5