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

问题描述:

-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