用合理的方法计算(1)21.7²-28.3²;(2)1.25×14²-125×8.6²2.当x=-3/5时,求(1-x)²-4(1-x²)+4(1+x)²的值.3.已知2x²-mx-5=(x-1)(2x+n),求m,n的值.
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![用合理的方法计算(1)21.7²-28.3²;(2)1.25×14²-125×8.6²2.当x=-3/5时,求(1-x)²-4(1-x²)+4(1+x)²的值.3.已知2x²-mx-5=(x-1)(2x+n),求m,n的值.](/uploads/image/z/8102660-68-0.jpg?t=%E7%94%A8%E5%90%88%E7%90%86%E7%9A%84%E6%96%B9%E6%B3%95%E8%AE%A1%E7%AE%97%EF%BC%881%EF%BC%8921.7%26%23178%3B-28.3%26%23178%3B%EF%BC%9B%EF%BC%882%EF%BC%891.25%C3%9714%26%23178%3B-125%C3%978.6%26%23178%3B2.%E5%BD%93x%3D-3%2F5%E6%97%B6%2C%E6%B1%82%EF%BC%881-x%EF%BC%89%26%23178%3B-4%EF%BC%881-x%26%23178%3B%EF%BC%89%2B4%EF%BC%881%2Bx%29%26%23178%3B%E7%9A%84%E5%80%BC.3.%E5%B7%B2%E7%9F%A52x%26%23178%3B-mx-5%3D%28x-1%29%282x%2Bn%29%2C%E6%B1%82m%2Cn%E7%9A%84%E5%80%BC.)
用合理的方法计算(1)21.7²-28.3²;(2)1.25×14²-125×8.6²2.当x=-3/5时,求(1-x)²-4(1-x²)+4(1+x)²的值.3.已知2x²-mx-5=(x-1)(2x+n),求m,n的值.
用合理的方法计算
(1)21.7²-28.3²;(2)1.25×14²-125×8.6²
2.当x=-3/5时,求(1-x)²-4(1-x²)+4(1+x)²的值.
3.已知2x²-mx-5=(x-1)(2x+n),求m,n的值.
用合理的方法计算(1)21.7²-28.3²;(2)1.25×14²-125×8.6²2.当x=-3/5时,求(1-x)²-4(1-x²)+4(1+x)²的值.3.已知2x²-mx-5=(x-1)(2x+n),求m,n的值.
21.7²-28.3² = (21.7+28.3)×(21.7-28.3) = 50×(-6.6) = -330
1.25×14²-125×8.6² = 1.25×14²-1.25×86² = 1.25×(14+86)×(14-86) = 125×(-72) = -9000