先化简,再求值:2(mn-3m²)+[m²-5(mn-m²)+2mn].其中m=1 n=-2

先化简,再求值:2(mn-3m²)+[m²-5(mn-m²)+2mn].其中m=1 n=-2
先化简,再求值:2(mn-3m²)+[m²-5(mn-m²)+2mn].其中m=1 n=-2

先化简,再求值:2(mn-3m²)+[m²-5(mn-m²)+2mn].其中m=1 n=-2
2(mn-3m²)+[m²-5(mn-m²)+2mn].
=2mn-6m²+m²-5m²+2mn
=4mn-10m²
=2m﹙2n-5m﹚
=2﹙﹣4－5﹚
=﹣18

=2mn-6m^2+m^2-5mn+5m^2+2mn
=2mn-5mn+2mn-6mn^2+m^2+5m^2
=-mn
=-1*(-2)
=2

去括号得2mn-6m的平方+m的平方-5mn+5m的平方+2mn。化简得-mn，代入得2