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【有奖解答】印度式乘法口诀的由来 by ericet

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· @ericet · (edited)
$4.24
【有奖解答】印度式乘法口诀的由来
<center><img src="https://cdn.pixabay.com/photo/2016/11/29/01/16/abacus-1866497_960_720.jpg" alt="" /><br/>
(Image source: <a href="https://cdn.pixabay.com/photo/2016/11/29/01/16/abacus-1866497_960_720.jpg">pixabay</a>)
</center>

之前分享了<a href="https://steemit.com/@ericet/tlu4prnaxp/#@steem-ua/re-tlu4prnaxp-20181224t225245z">印度式乘法口诀</a>,按照口诀的步骤我们可以很快的算出19x19以内的乘法。

前文回顾:

14    x  18 = ?
(被乘数) (乘数)

<ul>
<li>第一步:把被乘数跟乘数的个位数相加 14+8=22</li>
<li>第二步:把第一步的答案乘以10 22x10=220</li>
<li>第三步:把乘数的个位数乘以被乘数的个位数 8x4=32</li>
<li>第四步:被第二步和第三步的答案相加 (14+8)x10+(8x4)=252</li>
</ul>

大家有没有想过这个乘法口诀是怎么由来的吗?
今天我们用小学数学数到的内容来推算出这套口诀。

我们把19x19以内的按照数学公式来显示:
<img src="http://ericet.vornix.blog/wp-content/uploads/2018/12/W@KTCW65TIEJICA3LHC1S.png" alt="" /><br/>

从这套公式里面推算出来的结果就是上面说的印度式乘法的口诀。
不相信吗?我们一步步拆开来看。

<img src="http://ericet.vornix.blog/wp-content/uploads/2018/12/RPD1EA205V@1A0E.png" alt="" /><br/>

其实按照这套公式继续推算,可以推算出99x99以内所有乘法的口诀。

这部分留给大家来推算了
按照我上面推算的公式,推算出<strong>7a x 7b =?</strong> 的口诀,<strong>最快并且附上步骤</strong>的人将获得1 SBI的奖励。

大家快来推算吧~ 这不是送命,是送钱! <br /><center><hr/><em>Posted from my blog with <a href=&#039;https://wordpress.org/plugins/steempress/&#039;>SteemPress</a> : http://ericet.vornix.blog/2018/12/24/%e3%80%90%e6%9c%89%e5%a5%96%e8%a7%a3%e7%ad%94%e3%80%91%e5%8d%b0%e5%ba%a6%e5%bc%8f%e4%b9%98%e6%b3%95%e5%8f%a3%e8%af%80%e7%9a%84%e7%94%b1%e6%9d%a5/ </em><hr/></center>         
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@chloe1 ·
看到有正确答案了

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@ericet ·
下回加油💪

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@chloe1 ·
70×((70+a)+b)+ab
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@ericet ·
给出过程

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@chloe1 ·
第一步:把被乘数跟乘数的个位数相加 (70+a)+b
第二步:把第一步的答案乘以 ((70+a)+b)x70
第三步:把乘数的个位数乘以被乘数的个位数 axb
第四步:被第二步和第三步的答案相加 70x((70+a)+b)+ab
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@cnbuddy ·
吃了吗?还在发愁自己的好文没人发现,收益惨淡吗?记得加上cn-curation标签,让[飞鸽传书](https://steemit.com/@htliao/cn-curation-001-cn) 帮你走出困境吧!假如我的留言打扰到你,请回复“取消”。
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@mia-cc · (edited)
7ax7b=10x((70+a)+b)+ab
第一步:把被乘数跟乘数的个位数相加 (70+a)+b
第二步:把第一步的答案乘以10 ((70+a)+b)x10
第三步:把乘数的个位数乘以被乘数的个位数  axb
第四步:被第二步和第三步的答案相加  10x((70+a)+b)+ab
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@ericet ·
有一步错了,试着把过程展开

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@mia-cc ·
7ax7b=70x((70+a)+b)+ab
第一步:把被乘数跟乘数的个位数相加 (70+a)+b
第二步:把第一步的答案乘以70 ((70+a)+b)x70
第三步:把乘数的个位数乘以被乘数的个位数  axb
第四步:被第二步和第三步的答案相加  70x((70+a)+b)+ab
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@ericet ·
比如71x71=5041
按照你的步骤,(71+1)x10+1=721

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@steemstem ·
$0.85
re-ericet-cspm6cjkc2-20181225t172138972z
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👍  ,
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@tydebbie ·
大腦宣佈當機

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@wongshiying ·
1)7a x b
2) (7a x b) x10
3)  a x b
4) [(7a x b) x 10] + ab

是这样吗?

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@ericet ·
第一步错了,是7a+7b

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@zerofive ·
$0.02
7ax7b=(70+a)x(70+b)=4900+70x(a+b)+axb=70x((70+a)+b)+ab
👍  ,
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@ericet ·
正确✅

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@zerofive ·
@ericet  按照这样的步骤,算起来好像也不快
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@ericet ·
是的,只能在19x19内比较快

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