5m^2n-3n-5m^2n+n+2
=5m^2n-5m^2n-3n+n+2
=0-2n+2
=-2n+2
所以代数式5m^2n-3n-5m^2n+n+2的值与m无关,计算结果仅与n的取值有关,因此把m=2011看成了2001,或者m取任意数不影响代数式的值.