十字相乘做不对-8x²+14x-5,取-8=2*-4,-5=-1*5,2*5+-1*-4=14,正确.提(x-4)(x+5)=x²+x-20≠原式-8x²+14x-5,做错了
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![十字相乘做不对-8x²+14x-5,取-8=2*-4,-5=-1*5,2*5+-1*-4=14,正确.提(x-4)(x+5)=x²+x-20≠原式-8x²+14x-5,做错了](/uploads/image/z/6867907-43-7.jpg?t=%E5%8D%81%E5%AD%97%E7%9B%B8%E4%B9%98%E5%81%9A%E4%B8%8D%E5%AF%B9-8x%26%23178%3B%2B14x-5%2C%E5%8F%96-8%3D2%2A-4%2C-5%3D-1%2A5%2C2%2A5%2B-1%2A-4%3D14%2C%E6%AD%A3%E7%A1%AE.%E6%8F%90%28x-4%29%28x%2B5%29%3Dx%26%23178%3B%2Bx-20%E2%89%A0%E5%8E%9F%E5%BC%8F-8x%26%23178%3B%2B14x-5%2C%E5%81%9A%E9%94%99%E4%BA%86)
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十字相乘做不对-8x²+14x-5,取-8=2*-4,-5=-1*5,2*5+-1*-4=14,正确.提(x-4)(x+5)=x²+x-20≠原式-8x²+14x-5,做错了
十字相乘做不对
-8x²+14x-5,取-8=2*-4,-5=-1*5,2*5+-1*-4=14,正确.
提(x-4)(x+5)=x²+x-20≠原式-8x²+14x-5,做错了
十字相乘做不对-8x²+14x-5,取-8=2*-4,-5=-1*5,2*5+-1*-4=14,正确.提(x-4)(x+5)=x²+x-20≠原式-8x²+14x-5,做错了
提个负号.最后结果=-(x+1)(8x+5)