-2(mn-3m²)-[m²-5(mn-m²)+2mn],其中m=1,n=-2 快.

-2(mn-3m²)-[m²-5(mn-m²)+2mn],其中m=1,n=-2 快.
-2(mn-3m²)-[m²-5(mn-m²)+2mn],其中m=1,n=-2 快.

-2(mn-3m²)-[m²-5(mn-m²)+2mn],其中m=1,n=-2 快.
-2(mn-3m²)-[m²-5(mn-m²)+2mn]
=-2mn+6m²-m²+5(mn-m²)-2mn
=-4mn+5m²+5mn-5m²
=mn
=-2

=3m^2-2mn-m^2+5mn-5m^2-2mn
=mn-3m^2
=m(n-3m)
=-2-3
=-5