m^2=n+2,n^2=m+2 (m≠n),求：m^3-2mn=n^3的值．

“m^3-2mn=n^3”应该是“m^3-2mn+n^3”吧因为m^2=n+2,n^2=m+2 所以 m^2-n^2=n-m 即 (m-n)(m+n)=-(m-n) m+n=-1 m^3-2mn+n^3=m·m^2-2mn+n·n^2 =m(n+2)-2mn+n(m+2) =mn+2m-2mn+mn+2n =2(m+n) 因为m+n=-1 所以 原式=-2