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歡迎來到分數除法的教學課程

2
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讓我們開始吧

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在我教你們之前，事實上，我想要

4
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用不同的模組來教--我將教你

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如何做分數除法的技巧

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而你會發現這其實

7
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不會比分數乘法更難

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如果我問你，1/2除以1/2，不論何時

9
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當數字除以分數，或除以任何數字的時候

10
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就等於乘以這個數字的倒數

11
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所以，1/2除以1/2，就等於1/2乘以2/1

12
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我們剛剛把第二個1/2變為倒數

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我們從乘法模組知道，1/2乘以2/1

14
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就等於2/2

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或者就等於1

16
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這很合理，事實上，任何數字除以自己

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就等於1

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1/2除以1/2等於1，就像是5除以5等於1

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100除以100等於1

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這不是一個新的定律

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事實上，你過去總是如此做

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例如2除以2，你知道是1，但這不就像是2乘以2的倒數

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結果也是1

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我將演示給你看

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事實上，讓我多秀幾個例子

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讓你了解分數除法真的不是個新的觀念

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整個概念就是乘以它的倒數

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如果我問你12除以4是多少?

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當然我們知道答案是什麼，但是我要

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演示給你看，其實這跟12乘以1/4是一樣的

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12/1乘以1/4等於12/4，等於3

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而12/4就是12除以4的另一種書寫方式

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這就有點像是用比較複雜的方法來得到一樣的結果

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但是，我只是想讓你知道我們正在做的

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這個模組不是新的，其實就像是我們過去一直在做的

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當我們除以一個數字

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除法都是一樣的

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當除以一個數字，其實就等同於乘以

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那個數字的倒數

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復習一下倒數，當我有一個數字A

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它的倒數--就是1/A

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所以2/3的倒數是3/2，或者5的倒數

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因為5就等於5/1，所以5的倒數是1/5

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讓我們來做一些分數除法的問題吧

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2/3除以5/6是多少?

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我們知道，這就等同於2/3乘以6/5

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就等於12/15

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我們可以把分子及分母同時除以3，就等於4/5

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7/8除以1/4等於多少?

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這就等同於7/8乘以4/1

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記住，我剛剛翻轉了1/4

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除以1/4就等同於乘以4/1

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這就是你要解答分數除法的方式

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接著我們可以用一些在乘法模組

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學到的小捷徑

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8除以4等於2

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4除以4等於1

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所以答案就是7/2

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或者如果你想要把它寫成帶分數

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7/2是一個假分數

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假分數，它的分子

62
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會大於分母

63
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如果你想要把它寫成帶分數

64
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7除2等於3餘1，所以就是3 1/2

65
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兩種方式都可以

66
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我比較傾向用這個方式

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因為它比較容易做計算

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讓我們再多做幾題，或者是至少在接下來4~5分鐘裡面

69
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可以盡量多做一些

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-2/3除以5/2等於多少

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再一次，這就等於-2/3

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乘以多少?

73
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就等於乘以5/2的倒數，就是2/5

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所以就等於-4/15

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3/2除以1/6等於多少?

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這就等於3/2乘以6/1，就等於9

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我想你現在可能已經了解了

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讓我們看看，再多做幾題

79
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當然，你可以隨時暫停，再重新看一次這個課程

80
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然後再把看不懂的地方重看一遍

81
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讓我們來做 -5/7除以10/3

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這就等同於-5/7乘以3/10

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我剛剛把它乘以倒數

84
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這就是我剛剛一直重覆在做的

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-5乘以3

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-15

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7乘以10等於70

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如果我們把分子及分母

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同除以5，我們可以得到 -3/14

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我們也可以在這邊就這樣做

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我們可以除以5，得到2，同樣可以得到

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-3/14

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讓我們再做一兩個題目

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我想你已經有點了解了

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如果1/2除以-3

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啊哈

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所以，當一個分數除以一個正整數

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或者整數時會如何呢?

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我們知道任何正整數可以被寫做分數

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這就等於1/2除以-3/1

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而除以一個分數就等同於乘以

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它的倒數

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所以-3/1的倒數是-1/3

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所以就等於-1/6

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讓我們換個方式做

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如果-3除以1/2呢?

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一樣

108
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-3就等於-3/1，除以1/2

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就等於-3/1乘以2/1

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就等於 -6/1，等於-6

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現在，讓我給你一些理解

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為什麼這樣做會行得通

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如果說2除以1/3

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我們知道這就等於2/1乘以

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3/1，就等於6

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所以2、1/3、6之間有何關聯呢?

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讓我們這樣看這件事

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如果我有兩片比薩

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我有兩片比薩

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這裡是我的兩片比薩

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2在這邊

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所以如果我有兩片比薩，而我想要將它們

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分成很多個1/3片的比薩

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所以我把每片比薩都分成三等份

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我將要畫個小賓士符號

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所以我把每片比薩分成三等份，對吧?

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我有幾個1/3片的比薩呢?

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讓我們看看，1、2、3、4、5、6

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我有6個1/3片的比薩

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所以你可能想要坐下，然後思考一下

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但我想這可能對你來說有些許意義

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讓我們再做一題讓你的腦袋累一下

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假設-7/2除以-4/9

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這就等於-7/2乘以

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-9/4，對吧?

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我剛剛乘以-4/9的倒數

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9乘以7等於，-7乘以-9

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等於63，而2乘以4等於8

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我想你現在已經知道如何做分數的除法

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你可以試試

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分數除法的模組

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祝你學習愉快!