设sin18=x, cos36=cos2*18=1-2(sin18)^2=1-2x^2,(cos18)^2=1-x^2sin36=2xcos18sin18cos36+cos18sin36=cos36x(1-2x^2) +2x(1-x^2)=1-2x^24x^3-2x^-3x+1=04x^3-2x^-2x-x+1=0 2x(2x^2-x-1)-(x-1)=0 2x(2x+1)(x-1)-(x-1)...