一(m+n)^2+2mn(1-m-n)-1
二 x^2-xy+2x+y-3
一(m+n)^2+2mn(1-m-n)-1
二 x^2-xy+2x+y-3
问1
(m+n)^2+2mn(1-m-n)-1=(m+n)^2-1^2-2mn(m+n-1)
=(m+n+1)(m+n-1)-2mn(m+n-1)
=(m+n-1)(m+n+1-2mn)
问2
x^2-xy+2x+y-3 =(x^2+2x-3)-(xy-y) =(x+3)(x-1)-y(x-1) =(x-1)[(x+3)-y] =(x-1)(x+3-y)