若(x+m)(x-5)=x^2-2x+3n,则m-n=

问题描述:

若(x+m)(x-5)=x^2-2x+3n,则m-n=
正确结果是8,

(x+m)(x-5)=x^2-2x+3n
x²+(m-5)x-5m=x^2-2x+3n
所以:m-5=-2
-5m=3n
m=3
n=-5
m-n=3-(-5)=8