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