Question

八年级数学 一道关于整式化简的问题 要降次 不会做啊

Answer 1

m^3-2mn+n^3
=m(m^2-2n)+n^3
=m(2-n)+n(m+2)
=2m-mn+mn+2n
=2(n+m)

m^2=n+2，n^2=m+2
相减：
(m+n)(m-n)=-(m-n)
m≠n
m+n=-1
原式=2*(-1)=-2

Answer 2

m^3-2mn+n^3=m*m^2-2mn+n*n^2
=m(n+2)-2mn+n(m+2)
=mn+2m-2mn+mn+2n
=2m+2n=2(m+n)
又因为m^2=n+2 (1)
n^2=m+2 (2)
(1)-(2)，得
m^2-n^2=n-m，即
(m+n)(m-n)=-(m-n)
因为m≠n，所以m+n=-1
m^3-2mn+n^3=2(m+n)=-2
=2*(-1)=-2

Answer 3

m³-2mn+n³
=m³-mn+n³-mn
=m(m²-n)+n(n²-m)
将条件代入得m(n+-n)+n(m+2-m)
=2m+2n