1/2m^2+mn+1/2n^2
=1/2(m^2+2mn+n^2)
=1/2(m+n）²
因为m、n互为相反数,所以m+n=0
所以=1/2(m+n）²
=0
若m,n互为相反数,则1/2m^2+mn+1/2n^2的值是__0____