1、1/4x^2-xy+y^2
=(1/4)*(x²-4xy+4y²）
=(1/4)*(x-2y)²
2、36x^2y-48xy^2
=12xy(3x-4y)
3、y(x-y)^2-(y-x)^3
=y(x-y)^2 +(x-y)^3
=(y+x-y)(x-y)²
=x(x-y)²
4、-x^2y^2+z^2
=z²-x²y²
=(z+xy)(z-xy)