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[几何] 翻折后比较三个角

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realnumber posted 2019-2-14 21:17 |Read mode

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确认下，选D对吗？

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kuing posted 2019-2-14 22:51

易证 `\tan\theta:\tan\alpha=\csc\angle EAC`，又 `\angle EAC` 必须小于 30 度（否则不存在 `B'`），所以选项 D 是正确的。
至于其他选项，懒得举反例（越来越懒了

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