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在上一个视频中，我们讲了

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一个 30-60-90 的三角形的边长比

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是--如果我们假设最长的边是 x ，

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如果斜边是 x ，

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那么最短的边长就是 x/2，而这两个边之间的边，

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也就是60°角的对边，

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边长是 3x/2 的平方根。

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或者用另一种方法考虑，如果最短的边是 1，

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我先考虑最短的边，然后是长度居中的边，

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然后是最长的边。

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如果30°角对面的边长是 1，

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那么60°角对面的边长

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就是 它的3倍的平方根。

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它就是 3 的平方根。

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然后，斜边是它的2倍。

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上一个视频中，我们从 x 开始，

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我们说 30°对面的边是 x/2。

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但是，如果 30° 对面的边是 1，

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那么这条边就是它的 2倍。

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它就是 2。

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这里就是30°对面的边，

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60°对面的边，和斜边，也就是

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90°对面的边。

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一般来说，如果你看到

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任何三角形有这样的边长比，你就可以说，那是一个 30-60-90 的三角形。

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