原式x^4+2x^3+3x^2+2x+1 =x^4+2x^2+1+2x^3+x^2+2x =(x^2+1)^2+x^3+x+x^3+x^2+x =(x^2+1)^2+x(x^2+1)+x(x^2+x+1) =(x^2+1)(x^2+x+1)+x(x^2+x+1) =(x^2+1+x)(x^2+1+x) =(x^2+1+x)^2