题目内容
化简求值:
(1) 3a2﹣[7a2﹣2a﹣(3a2﹣3a)+1],其中a=.
(2) 2(3m2﹣mn)﹣[m2﹣5(mn﹣m2)+2mn],其中m=1,n=﹣2.
(1) 3a2﹣[7a2﹣2a﹣(3a2﹣3a)+1],其中a=.
(2) 2(3m2﹣mn)﹣[m2﹣5(mn﹣m2)+2mn],其中m=1,n=﹣2.
解:(1)原式=3a2﹣[7a2﹣2a﹣3a2+3a+1]
=3a2﹣7a2+2a+3a2﹣3a﹣1
=﹣a2﹣a﹣1;
将a=代入可得:原式=﹣a2﹣a﹣1=﹣;
(2)原式=6m2﹣2mn﹣[m2﹣5mn+5m2+2mn]
=6m2﹣2mn﹣m2+5mn﹣5m2﹣2mn
=mn;
将m=1,n=﹣2代入可得:原式=mn=﹣2.
=3a2﹣7a2+2a+3a2﹣3a﹣1
=﹣a2﹣a﹣1;
将a=代入可得:原式=﹣a2﹣a﹣1=﹣;
(2)原式=6m2﹣2mn﹣[m2﹣5mn+5m2+2mn]
=6m2﹣2mn﹣m2+5mn﹣5m2﹣2mn
=mn;
将m=1,n=﹣2代入可得:原式=mn=﹣2.
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