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

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

已知 m-n=4,mn=-1 .求(-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn)的值
(-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
=3(m-n-2mn)
原式=3[4-2(-1)]
=3×6=18
应该是这样

原式=-2mn+2m+3n-3mn-2n+2m-m-4n-mn
=(-2mn-3mn-mn)+(2m+2m-m)+(3n-2n-4n)
=-6mn+3m+(-3n)
=-6mn+3m-3n
=-6mn+3(m-n)
m-n=4,mn=-1
原式=-6mn+3(m-n)=-6×(-1)+3×4=18