先化简,再求值:2a²+3ab+b²-a²-ab-2b²,其中a²-b²=2,ab=-3
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![先化简,再求值:2a²+3ab+b²-a²-ab-2b²,其中a²-b²=2,ab=-3](/uploads/image/z/1268166-30-6.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%2C%E5%86%8D%E6%B1%82%E5%80%BC%3A2a%26%23178%3B%2B3ab%2Bb%26%23178%3B-a%26%23178%3B-ab-2b%26%23178%3B%2C%E5%85%B6%E4%B8%ADa%26%23178%3B-b%26%23178%3B%3D2%2Cab%3D-3)
先化简,再求值:2a²+3ab+b²-a²-ab-2b²,其中a²-b²=2,ab=-3
先化简,再求值:2a²+3ab+b²-a²-ab-2b²,其中a²-b²=2,ab=-3
先化简,再求值:2a²+3ab+b²-a²-ab-2b²,其中a²-b²=2,ab=-3
2a²+3ab+b²-a²-ab-2b²
=2a²-a²-2b²+b²+3ab-ab
=a²-b²+2ab
代入a²-b²=2,ab=-3得
原式=2+2x(-3)
=-4
化简之后为:a²+2ab-b²
答案:-4
2a²+3ab+b²-a²-ab-2b²=a^2-b^2+2ab
a²-b²=2,ab=-3时,
2a²+3ab+b²-a²-ab-2b²=2+2x(-3)=-4
=a^2-b^2+2ab
=2+2*(-3)
=-4
2a²+3ab+b²-a²-ab-2b²
=2a²-a²-2b²+b²+3ab-ab
=a²-b²+2ab
代入a²-b²=2,ab=-3得
原式=2+2x(-3)
=-4