2m(m-n)-(m+2n)(2m-n)
=2m^2-2mn-(2m^2+3mn-2n^2)
=2m^2-2mn-2m^2-3mn+2n^2
=2m^2-2m^2+2n^2-2mn-3mn
=2n^2-5mn
=2*(-2)^2-5*1*(-2)
=8+10
=18
先化简再求值:2m(m-n)-(m+2n)(2m-n),其中m=1,n=-2
先化简再求值:2m(m-n)-(m+2n)(2m-n),其中m=1,n=-2
数学人气：334 ℃时间：2020-06-28 08:35:12
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