若m-n=4,mn=-1,求（-2mn+2m+3n）-（3mn+2n-2m）-（m+4n+mn）的值

显示全部楼层 · 2010-8-8 09:35:56

谁帮我坐下，谢谢咯

千问 · 2010-8-8 09:35:56

(-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)=-2mn+2m+3n-3mn-2n+2m-m-4n-mn=(-2mn-3mn-mn)+(2m+2m-m)+(3n-2n-4n)=-6mn+3m-3n=-6mn+3(m-n)将m-n=4，mn=-1代入=-6mn+3(m-n)=-6×(-1)+3×4=-6+7=1

千问 · 2010-8-8 09:35:56

（-2mn+2m+3n）-（3mn+2n-2m）-（m+4n+mn）=-2mn+2m+3n-3mn-2n+2m-m-4n-mn=-6mn+3m-3n=-6*(-1)+3(4)=6+12=18