先化简,再求值:3a2b-{2a2b+[9a2b-2(6a2b+4a2)]-(3a2b-8a2)},其中a=-12,b=-2.-数学

题目简介

先化简,再求值:3a2b-{2a2b+[9a2b-2(6a2b+4a2)]-(3a2b-8a2)},其中a=-12,b=-2.-数学

题目详情

先化简,再求值:3a2b-{2a2b+[9a2b-2(6a2b+4a2)]-(3a2b-8a2)},其中a=-
1
2
,b=-2.
题型:解答题难度:中档来源:不详

答案

3a2b-{2a2b+[9a2b-2(6a2b+4a2)]-(3a2b-8a2)}
=3a2b-{2a2b+[9a2b-12a2b-8a2]-3a2b+8a2},
=3a2b-{2a2b+9a2b-12a2b-8a2-3a2b+8a2},
=3a2b-2a2b-9a2b+12a2b+8a2+3a2b-8a2
=7a2b
当a=-class="stub"1
2
,b=-2时,
原式=7×(-class="stub"1
2
)2×(-2)=class="stub"7
2

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