ab(x2-y2)+xy(a2-b2)
问题描述：
ab(x2-y2)+xy(a2-b2)
答
原式
=abx^2-aby^2+xya^2-xyb^2
=abx^2+a^2xy-(by^2a+b^2xy)
=ax(bx+ay)-by(ay+bx)
=(ax-by)(ay+bx)