先化简,再求值:5(3a²b-ab²)-4(-ab²+3a²b)其中a=1/2,
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先化简,再求值:5(3a²b-ab²)-4(-ab²+3a²b)其中a=1/2,b=-1/3
![先化简,再求值:5(3a²b-ab²)-4(-ab²+3a²b)其中a=1/2,](/uploads/image/z/7300415-47-5.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%2C%E5%86%8D%E6%B1%82%E5%80%BC%3A5%283a%26%23178%3Bb-ab%26%23178%3B%29-4%28-ab%26%23178%3B%2B3a%26%23178%3Bb%29%E5%85%B6%E4%B8%ADa%3D1%2F2%2C)
解
5(3a²b-ab²)-4(-ab²+3a²b)
=(15a²b-12a²b)+(-5ab²+4ab²)
=3a²b-ab²
=ab(3a-b)
=1/2×(-1/3)(3×1/2+1/3)
=-1/6×(3/2+1/3)
=-1/6×11/6
=-11/36
5(3a²b-ab²)-4(-ab²+3a²b)
=(15a²b-12a²b)+(-5ab²+4ab²)
=3a²b-ab²
=ab(3a-b)
=1/2×(-1/3)(3×1/2+1/3)
=-1/6×(3/2+1/3)
=-1/6×11/6
=-11/36
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