Question

Решите пример, не получается

Answer 1

sinπ/18*cosπ/9*cos2π/9=(2cosπ/18*sinπ/18*cosπ/9*cos2π/9)/(2cosπ/18)=
=(sinπ/9*cosπ/9*cos2π/9)/(2cosπ/18)=(sin2π/9*cos2π/9)/(4cosπ/18)=
=(sin4π/9)/(8cosπ/18)=(sin(π/2-π/18))/(8cosπ/18)=(cosπ/18)/(8cosπ/18)=1/8