x的四次方减4x的三次方加2x的平方加4x加1=x^4-4x^3+2x^2+4x+1=x^4-2x^3-x^2-2x^3+4x^2+2x-x²+2x+1=x^2(x²-2x-1)-2x(x²-2x-1)-(x²-2x-1)=(x²-2x-1)²