有趣的数学【11】：捧着金饭碗要饭 by kissfirer

steempress · @kissfirer · Jan 15 '19

$4.31

有趣的数学【11】：捧着金饭碗要饭

讲一个人没有自知之明，多数是说这个人过高地估计了自己的能力，不懂得量力而行，量体裁衣。而实际上，自知之明的意思是：
<blockquote>自己不了解自己，不知道自己的长处和短处，没有能够正确地认识自己。
</blockquote>
有些人，自己拥有超人的能力而不自知，这也属于没有自知之明。这其实是极大的浪费，正所谓千里马常有，而伯乐不常有。

<strong>像这样的人，就会干出捧着金饭碗去要饭的事情。</strong>

在数学的世界里，这样的人有很多。

就像所有的同学都学了很多基本的数学公式与定理，但是有些人理解了，还能灵活运用；但有些人虽然记住了，但完全不会用，看到题目不会做。这就好比是捧着金饭碗去要饭——所有必要的条件都具备了，但利用不起来。
<p><strong>比如，我们都知道的韦达定理，说明了一元二次方程中根和系数之间的关系。用数学表达式写出来，是这样的：</strong>
设一元二次方程ax²+bx+c=0（a，b，c均为实数，a≠0） 中，两根x₁、x₂有如下关系：</p>
<center><strong>x1 + x2 = -b/a；</strong>
<strong>x1 × x2 = c/a；</strong></center></p>


<hr />

像下面这道题，就是利用韦达定理求解，可惜有的人把韦达定理背得滚瓜烂熟，却不会用：
![image](https://ipfs.busy.org/ipfs/QmUFNzo1kRTXsnrZXQmDH9YdZwL911Fgxy2Htfrth92p2o)

因为x，y为实数，那么z也为实数。

我们把这2个算式看做是一个一元二次方程的韦达定理表现形式，则该一元二次方程的的系数：
a = 1，
b = -（5-z）；
c = z²-5z+3；

则该一元二次方程为：
![image](https://ipfs.busy.org/ipfs/QmRokiEJPBbUd6pmGywQVwaWnEwrYptiDKDL1Cg3RsrgZb)

<hr />

<strong>这时，就又需要利用到一元二次方程根的判别式了，这也是所有的同学都知道的定律：</strong>
![image](https://ipfs.busy.org/ipfs/QmQVjdftT8g5JCXPcRLrQC78MyvKkJqbPgbUAmuzNPaRpQ)
进一步整理，可得：
3z²-10z-13 ≤ 0

利用十字相乘法进行因式分解，可得：
(z+1)(3z-13) ≤ 0

这种情况下，方程解有2种情况：
![image](https://ipfs.busy.org/ipfs/QmYBUUNka8W6BVu999BRyJkk4zZfBhqz2raj5hh6hSREWb)
<strong>这样，就求出了z的最大值为13/3。</strong>

***
这就是人与人之间的差别：
<strong>学到的内容是一样的，但是由于每个人的认知不同，有些人很快就能解决问题，而有些人却只能捧着金饭碗去要饭，可悲啊！！</strong>

希望你不是那个捧着金碗要饭的人。

***
附上解题过程草稿纸：
![image](https://ipfs.busy.org/ipfs/QmfUF6c1mW5zfNZE7iaFhRW8QimKwtxj55dvz1tUfWY6sd)

***
参考：
[百度百科：韦达定理](https://baike.baidu.com/item/%E9%9F%A6%E8%BE%BE%E5%AE%9A%E7%90%86/105027?fr=aladdin)

[百度百科：一元二次方程](https://baike.baidu.com/item/%E4%B8%80%E5%85%83%E4%BA%8C%E6%AC%A1%E6%96%B9%E7%A8%8B) <br /><center><hr/><em>Posted from my blog with <a href='https://wordpress.org/plugins/steempress/'>SteemPress</a> : https://kissfirer.000webhostapp.com/maths11 </em><hr/></center>

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@minnowsupport · Jan 15 '19

<p>Congratulations!  This post has been upvoted from the communal account, @minnowsupport, by killer from the Minnow Support Project. It's a witness project run by aggroed, ausbitbank, teamsteem, someguy123, neoxian, followbtcnews, and netuoso. The goal is to help Steemit grow by supporting Minnows.  Please find us at the <a href="https://discord.gg/HYj4yvw"> Peace, Abundance, and Liberty Network (PALnet) Discord Channel</a>.  It's a completely public and open space to all members of the Steemit community who voluntarily choose to be there.</p> <p>If you would like to delegate to the Minnow Support Project you can do so by clicking on the following links: <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=102530.639667%20VESTS">50SP</a>, <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=205303.639667%20VESTS">100SP</a>, <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=514303.639667%20VESTS">250SP</a>, <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=1025303.639667%20VESTS">500SP</a>, <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=2053030.639667%20VESTS">1000SP</a>, <a href="https://v2.steemconnect.com/sign/delegateVestingShares?delegator=&amp;delegatee=minnowsupport&amp;vesting_shares=10253030.639667%20VESTS">5000SP</a>. <br><strong>Be sure to leave at least 50SP undelegated on your account.</strong></p>

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@steemitboard · Jan 15 '19

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@cnbuddy · Jan 15 '19

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@steemstem · Jan 15 '19

re-kissfirer-11-rjztkpqsri-20190115t235202970z

<div class='text-justify'> <div class='pull-left'> <br /> <center> <img width='125' src='https://i.postimg.cc/9FwhnG3w/steemstem_curie.png'> </center>  <br/> </div> <br /> <br /> 

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 If you appreciate the work we are doing then consider [voting](https://www.steemit.com/~witnesses) both projects for witness by selecting [**stem.witness**](https://steemconnect.com/sign/account_witness_vote?approve=1&witness=stem.witness) and [**curie**](https://steemconnect.com/sign/account_witness_vote?approve=1&witness=curie)! <br /> 
For additional information please join us on the [**SteemSTEM discord**]( https://discord.gg/BPARaqn) and to get to know the rest of the community! </div>

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