(2x-y)(x+y)-(4x-5y)-6=(2x-y+2)(x+y-3) 为什么这么做,原理是什么?

(2x-y)(x+y)-(4x-5y)-6=(2x-y+2)(x+y-3) 为什么这么做,原理是什么?
(2x-y)(x+y)-(4x-5y)-6=(2x-y+2)(x+y-3) 为什么这么做,原理是什么?

(2x-y)(x+y)-(4x-5y)-6=(2x-y+2)(x+y-3) 为什么这么做,原理是什么?
(2x-y)(x+y)-(4x-5y)-6
=(2x-y)(x+y)-3(2x-y)+2(x+y)-6
=(2x-y+2)(x+y-3)
把2x-y看成m x+y看成n
mn-3m+2n-6
=m(n-3)+2(n-3)
=(m+2)(n-3)