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

问题描述:

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+5mn-5m²-2mn
=mn
=1x-2
=-2