Преобразуйте выражение, пожалуйста...
sin 4π/25 * cos π/25 + cos 4π/25 * sin π/25/cos 2π/5 * cos π/15 + sin 2π/5 * sin π/15

(sin 4π/25 * cos π/25 + cos 4π/25 * sin π/25)/(cos 2π/5 * cos π/15 + sin 2π/5 * sin π/15)=sin(4π/25+π/25)/cos(2π/5-π/15)=sin(π/5)/cos(π/3)=sin(π/5):1/2==2sin(π/5)