4|m+n|+4m^2+1=4m
即4|m+n| +4m^2-4m+1=0
4|m+n|+(2m-1)^2=0
根据非负数的性质:
m+n=0
2m-1=0
即m=1/2,n=-1/2
(m-n)^2=[1/2-(-1/2)]^2=1