cosπ/9*cos2π/9*cos3π/9*cos4π/9=(cosπ/9*cos2π/9*cos3π/9*cos4π/9)*8(sinπ/9)/8（sinπ/9）∵2cosπ/9*sinπ/9=sin2π/9∴原式=(4sin2π/9*cos2π/9*cos3π/9*cos4π/9)/8（sinπ/9）∵2sin2π/9*cos2π/9...