分解因式3x的四次方-9x的三次方-27x²-81x
=3x(x^3-3x^2-9x-27)
=3x(x^2(x-3)-9(x+3))
分解因式x²-x²y+xy²-x+y-y²
=x²(1-y)+x(y²-1)+y(1-y)
=(x²+y)(1-y)+x(y-1)(y+1)
=(x²+y)(1-y)-x(1-y)(y+1)
=(x²+y-xy-x)(1-y)
=[x(x-1)-y(x-1)](1-y)
=(x-y)(x-1)(1-y)
分解因式x²-4x+y²+2xy-4y+4
=(x+y)²-4(x+y)+4
=(x+y-2)²