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现在我们开始讲立体几何体积问题

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如图是一个三棱柱

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由三角形组成的立体图形

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有好几种

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这是三棱柱

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三棱柱两端有两个隔开的三角形

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其余各面是矩形

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另一种跟三角形相关的立体图形

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就是金字塔

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这就是一个四棱锥

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因为它的底是矩形或正方形

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也有三棱锥形

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每个面都是三角形

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但这一题是三棱柱

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我不想讲太多的形状分类问题

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如果三角形的底b长为7

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三角形的高h为3

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三棱柱长l为4

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求三棱柱的体积

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已知底为7

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因此三角形的底为7

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三角形的高为3

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因此这个距离

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h等于3

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棱柱的长为4

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那我就假设这个边

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这条边长为4

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边长为4

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在这个情况下 你需要做的就是

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算出这个三角形的面积

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我们可以先算出这个三角形的面积

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然后再乘以有多深

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也就是乘以棱柱的长度

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那体积就是这个三角形的面积

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我把三角形涂成粉色

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这个三角形的面积

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我们知道三角形的面积就是

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底乘以高除以二

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那么面积

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就是这个三角形的面积

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底乘以高除以二

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然后再乘以三棱柱的长

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棱柱的长为4

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那就再乘以

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乘以4

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乘以这个长度

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也就是乘以4

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那么我们就得到

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1/2乘以4等于2

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这两项约掉了 只剩下2

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然后2乘以3等于6

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6乘以7等于

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6乘以7等于42

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单位是立方

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如果这些单位是厘米的话

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那结果就是立方厘米

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但是题目没有告诉我们单位

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再做讲一题

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如图是一个立方体

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假设每条边x都是3

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求立方体的体积

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每条边都相等

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且长为3

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因此这条边是3

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这条边也是3

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每条边都是3

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这题其实和三棱柱那题一样

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而且立方体还更好做

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只需要求出这个面的面积就好了

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这个很简单

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这是一个正方形

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面积就是底乘高

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这里底和高相等 就是3乘以3

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那么体积就是这个面的面积

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3乘以3

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再乘以长

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乘以长

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长为3

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就乘以3

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因此就是3乘以3乘以3

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结果是27

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如果你懂指数

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就是3的三次方

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这就是为什么在三次方的时候

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人们说立方

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因为求立方体的体积

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找到这个边长

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乘以三次

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每个数代表一个维度

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分别代表长 宽 高

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长或深

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看你想怎么理解了

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因此就是3乘3乘3