WEBVTT

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要解二次方程 －3x 的平方加上

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10x 减去 3 等于 0。

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这个方程已经是标准式了。

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有很多解法。

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如果采用二次方程求解的公式一定可以解出来。

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我把方程抄下来。

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方程为－3x 的平方加上 10x 减去 3 等于 0。

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我打算用二次方程的公式

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来解两次，以说明只要我们

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正确地使用公式，

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就一定能得到该

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方程的正确且

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一致的解答。

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在眼前这个格式的方程里面, a, b, c 是多少？

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我们先来谈谈二次方程

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的解题公式是什么。

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从这里开始比较好。

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二次方程的解题公式

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就是面对一个二次方程，

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格式为 a x 平方加上 b x 再加上 c 等于 0，就是用标准格式来表示，

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它的解就是 x 等于 －b

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加上或减去 b 的平方减去 4a c的平方根，

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然后再除以 2a。

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而这个公式源于解二次方程的

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构建平方法。

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因此这个方法并不深奥，我在其它的视频里已经推导过了。

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这就是解二次方程的公式。

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这个公式可以得到两个解，

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因为这里有正负

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两个平方根。

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在这里把它应用于本例 － 本例里面，

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a 等于 －3，b 等于 10，

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c 等于 －3。

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所以在这里运用解二次方程的公式，

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所得的解为 x 等于一个代数式，

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其分子部分第一项 －b，b 就是 10。

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－b 就是 －10，然后加或减一个根式，

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里面第一项是 b 平方。

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