计算.(1)3a²-2a+4a²-7a (2)1/2st+4+3st-4 (3)2(2ab+3a)-3(2a-ab)(4)a²-【-4ab+(ab-a²)】-2ab
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![计算.(1)3a²-2a+4a²-7a (2)1/2st+4+3st-4 (3)2(2ab+3a)-3(2a-ab)(4)a²-【-4ab+(ab-a²)】-2ab](/uploads/image/z/765116-44-6.jpg?t=%E8%AE%A1%E7%AE%97.%EF%BC%881%EF%BC%893a%26%23178%3B-2a%2B4a%26%23178%3B-7a+%EF%BC%882%EF%BC%891%2F2st%2B4%2B3st-4+%EF%BC%883%EF%BC%892%EF%BC%882ab%2B3a%EF%BC%89-3%EF%BC%882a-ab%EF%BC%89%EF%BC%884%EF%BC%89a%26%23178%3B-%E3%80%90-4ab%2B%EF%BC%88ab-a%26%23178%3B%EF%BC%89%E3%80%91-2ab)
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计算.(1)3a²-2a+4a²-7a (2)1/2st+4+3st-4 (3)2(2ab+3a)-3(2a-ab)(4)a²-【-4ab+(ab-a²)】-2ab
计算.(1)3a²-2a+4a²-7a (2)1/2st+4+3st-4 (3)2(2ab+3a)-3(2a-ab)
(4)a²-【-4ab+(ab-a²)】-2ab
计算.(1)3a²-2a+4a²-7a (2)1/2st+4+3st-4 (3)2(2ab+3a)-3(2a-ab)(4)a²-【-4ab+(ab-a²)】-2ab
3a²-2a+4a²-7a =﹙3+4﹚a²+﹙-2-7﹚a=7a²-9a
1/2st+4+3st-4=3.5st
2(2ab+3a)-3(2a-ab﹚=4ab+6a-6a+3ab=7ab
a²-【-4ab+(ab-a²)】-2ab
=a²-﹙-4ab+ab-a²﹚-2ab
=a²+3ab+a²-2ab
=2a²+ab