一道计算题 先化简,后求值-2(mn-3m²)-{m²-5(mn-m²)+2mn},其中m=1,n=2

问题描述:

一道计算题 先化简,后求值
-2(mn-3m²)-{m²-5(mn-m²)+2mn},其中m=1,n=2

-2(mn-3m²)-{m²-5(mn-m²)+2mn}
=mn=2

-2(mn-3m²)-{m²-5(mn-m²)+2mn}
=-2mn+6m²-m²+5(mn-m²)-2mn
=-4mn+5m²+5mn-5m²
=mn
=2

Fate木棉 先化简:-2(mn-3m²)-[m²-5(mn-m²)+2mn]=-2mn+6m²-(m²-5mn+5m²+2mn)=-2mn+6m²-(6m²-3mn)=-2mn+6m²-6m²+3mn=mn∴当m=1,n=2时原式=1×2=2