5x^2-4y+xy-20x
问题描述：
5x^2-4y+xy-20x
答
5x^2-4y+xy-20x
=5x^2-20x-4y+xy
=5x(x-4)-y(4-x)
=5x(x-4)+y(x-4)
=(x-4)(5x+y)