m和n互为相反数,m=-n
m³+n³=(m+n)(m²-mn+n²)=0
m,n≠0,m/n=-1
xy互为倒数,x=1/y xy=1
xy(m³+n³)-m÷n +x²y²
=0-(-1)+(xy)²
=1+1
=2