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本集视频 我将想大家介绍

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一些常见角的术语

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我想给大家介绍的术语就是

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锐角 直角和钝角

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当我们讲这些术语时

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这些术语其实是不言自明的

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锐角就是

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我先把这些角画出来

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这样的话

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大家就明白是什么意思了

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锐角看起来就是这样的

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我画两条射线

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它们从同一点出发

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我还可以

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锐角可以是旁边这个角

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我还可以这样画锐角

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就是两条直线相交形成的角

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这个角就是锐角

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这个角也是锐角

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这两个角都是锐角

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我们把锐角看做是

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因为还没有定义直角

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比直角小

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可以看出 锐角比直角小

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直角就是 两条射线或直线

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相互垂直

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但这两条线

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如果一条是水平方向的

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另一条就是垂直方向的

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我先用射线画

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直角就是

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这一条线从左到右

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另一条线从上到下

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这个角就是直角

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我可以这样标识这个角

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这是角的通用标识方法

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但直角的标识方法是

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画一个小直角

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就是个小矩形的一半

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这就表明这个角是直角

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或者说 如果这条线从左到右的话

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这条线就是从上到下

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这个角是

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这个完全是

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我想解释它为什么叫直角

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的最佳方法是

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和下边这条线相比

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这条射线是垂直的

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让我再画一些线

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如果画一条这样的线

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再画这样一条线

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这个角就是直角

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其实这四个角都是直角

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这就意味着这条线完全

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如果这个是底的话

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与底这条线相比

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这条线是完全垂直

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这四个角中的任意一个

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都是直角

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既然已经定义了直角

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我就可以给锐角再下一个定义

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锐角就是

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比直角小的角

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在学了弧度和角度

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这是两种度量角度的方式后

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你就会知道

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直角就是90°

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这个角就小于90°

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这个角小于90°

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理解锐角的其它方法是

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锐角的开口小 更窄

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这两条线跟直角相比

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你只需要转动其中一条线一点儿

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就可与另一条线重合

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而直角

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你需要转动这么远

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而锐角你只需要转动一点

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因此锐角比直角小

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你可能已经开始想

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钝角是什么了

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钝角比直角大

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让我画几个钝角

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钝角看起来是

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让我画清楚点

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看起来可能是这样

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如果这是一个直角的话

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另外一条线

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可能是这样的

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与底相比的话

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是完全垂直的

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但是不是这样的

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这条橙色的射线

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开口比直角更大

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因此是钝角

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这术语其实是来自日常用语

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锐 代表 锋利或敏锐

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钝 代表 不锋利或不敏锐

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你可以它看成是个锋利的尖儿

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开口不是很大

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与其它相比

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这个更敏锐

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我也不知道 我只是帮大家做些联想

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钝角不敏锐

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这个又大又开

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不可能感知到细小的东西

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可能这个比较不大合适

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但理解它的一个方法就是

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钝角开口大

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比直角大

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大于90°

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大于90°

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如果想量这个角的话

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与直角相比的话

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你需要转动更多

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以到达另外一条射线

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毫无疑问 比锐角大得更多

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如果用直线画这些角

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哪些是直角 哪些是钝角？

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我这样画的

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这两个角是锐角

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锐角

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这两个角就是钝角

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这个角和这个角

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这两个角是钝角

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上边其实我也画了钝角

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这两个角也是钝角

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很简单

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如果一条直线或射线

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与另外一条

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上下方向

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与左右方向垂直

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或是完全垂直

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那么这就是直角

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如果两条线开口小

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转动的比较少

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那就是锐角

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如果转动的多

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那就是钝角

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如果看到它们

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很容易就区分出这几个角