x4－2y4－2x3y＋xy3为什么不能这样算?原式=x3(x-2y)-y3(2y-x)=x3(x-2y)+y3(x-2y)=(x_数学解答

x4－2y4－2x3y＋xy3
为什么不能这样算?
原式=x3(x-2y)-y3(2y-x)
=x3(x-2y)+y3(x-2y)
=(x-2y)(x3+y3)
另外：x3-y3的公式是?

人气：342 ℃　时间：2020-04-30 09:12:10

解答

原式=x3(x-2y)-y3(2y-x)
=x3(x-2y)+y3(x-2y)
=(x-2y)(x3+y3)
=(x-2y)(x+y)(x2-xy+y2)
x3-y3=(x-y)(x2+xy+y2)
x3+y3=(x+y)(x2-xy+y2)