已知m^2=n+2,n^2=m+2(m不等于n）求m^3-2mn+n^3的值.

m^2=n+2,n^2=m+2
m^2+m^2=m+n+4
m^2-n^2=(m+n)(m-n)=n-m
=>m+n=-1
m^2+n^2=m+n+4=3
mn=1/2*[(m+n)^2-(m^2+n^2)]=-1
代入
m^3-2mn+n^3
=(m^3+n^3)-2mn
=(m+n)(m^2-mn+n^2)-2mn
=(m+n)(m+n+4-mn)-2mn
=-1*(3+1)+2
=-4+4
=-2