求0.3m²n-1/5mn²+0.4n²m-m²n-1/2m²n的值,其中丨m-1/2丨+（n+1)²=0
问题描述：
求0.3m²n-1/5mn²+0.4n²m-m²n-1/2m²n的值,其中丨m-1/2丨+（n+1)²=0
答
m=1/2
n=-1
原式=-1.2m²n+0.2n²m
=0.3+0.1=0.4