这道这道数学题怎么做？

来源：蜘蛛抓取(WebSpider) 时间：2014-12-13 15:42 标签： 这道题怎么做 英文
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这道题怎么做？
f(x)=x^2-mInx,h(x)=x^2-x+a
（1）当a=0时，f(x)&=h(x)在(1,无穷大)上恒成立，求实数m的取值范围
（2）当m=2时，若函数k(x)=f(x)-h(x)在[1,3]上恰有两个不同零点，求实数a的取值范围。
设函数f(x)=x^2-mInx,h(x)=x^2-x+a
（1）当a=0时，f(x)&=h(x)在(1,无穷大)上恒成立，求实数m的取值范围
解：x^2-mInx&=x^2-x,x∈（1，+∞），
∴lnx&0,m&=x/lnx,记为g(x),
g'(x)=[lnx-1]/(lnx)^2,由g'(x)=0得x=e,
g(x)|min=g(e)=e,
∴m&=e,为所求。
（2）当m=2时，若函数k(x)=f(x)-h(x)在[1,3]上恰有两个不同零点，求实数a的取值范围。
解：k(x)=x^2-2lnx-(x^2-x+a）=x-a-2lnx,
k'(x)=1-2/x,由k'(x)=0得x=2.
k(x)|min=k(2).
k(x)在[1,3]上恰有两个不同零点，
&==&{k(2)=2-a-2ln2&0,
{k(1)=1-a&=0,
{k(3)=3-a-2ln3&=0.
&==&{a&2-2ln2,
{a&=3-2ln3.
∴2-2ln2&a&=3-2ln3,为所求。
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提问者采纳
456*3*=456*123**456*1001001=456*123*（1001）=456*123*0=0
提问者评价
你的回答完美的解决了我的问题，谢谢！
来自：作业帮
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出门在外也不愁这道题怎么做：阅读下面的材料，然后_百度知道
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阅读下面的材料，然后根据材料内容回答所提问题。
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&&&& There were 30 children in the classroom and all were trying to think about not only what they did, but also
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&&&& "Uh, Oh." I thought. I was the one who broke the window with a football. I did not mean to do it. I would
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&&&& Miss Green went to the bookshelf and took down a book.
&&&& "I know how you like birds, Peter." She said. "Here is a book about birds and the book is yours now. I will
not punish you this time. But Peter, you should remember that I am rewarding (奖赏) you for your honesty (诚 实), not for breaking the window."
&&&& I couldn't believe it! The teacher didn't punish me and I was getting my very favorite book. Now, I still use
that book, and it always reminds me of (使我想起) the lesson my teacher taught me.
&&&& Honesty is always best.
1. Who broke the window?
&&& ________________________________________________________ 2. How many children were in the classroom?& &&& ________________________________________________________ 3. Where did Miss Green take down the book?& &&& ________________________________________________________ 4. What was the book about?& &&& ________________________________________________________ 5. What can we learn from the story?& &&& ________________________________________________________
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3. The bookshelf.
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5. Honesty is always best.
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这道题怎么做？？
可知 Q = c * m * (T1- T2)
Q为热量的转换、c为水的比热， m为水的质量，
(T1- T2)为水温的变化量
根据热力学第一定律，假设没有热量流失，则热水放出的热量等于冷水吸收的热量。
c * m冷 * (T1- T2)冷 = c * m热 * (T1- T2)热
设用冷水X千克，则
x * (40-20) * c = (120-X) * (80-40) * c
60X = 4800
用 80 千克20度冷水和 40 千克80度热水混合，可得到40度的温水120千克
=M2△T2
冷水升温20度，热水降温40度，就有
20M1=40M2
&&&&&&&&&& （1）
由题意还有：
M1+M2=120 &&&&&&&&&& （2）
联立（1）、（2）就可得到：M1=80（Kg)
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