Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
Chứng minh \(\frac{1}{\left(n+1\right)\sqrt{n}+n\sqrt{n+1}}=\frac{1}{\sqrt{n}}-\frac{1}{\sqrt{n+1}}\) rồi áp dụng với n = 1,2,....,2014
![](https://rs.olm.vn/images/avt/0.png?1311)
Mỗi biểu thức trong dấu căn có dạng:
\(1+\frac{1}{k^2}+\frac{1}{\left(k+1\right)^2}\) ( Với \(k\ge2\))
Ta có:
\(1+\frac{1}{k^2}+\frac{1}{\left(k+1\right)^2}=\frac{k^2\left(k+1\right)^2+\left(k+1\right)^2+k^2}{k^2\left(k+1\right)^2}=\frac{k^4+2k^3+k^2+k^2+2k+1+k^2}{k^2\left(k+1\right)^2}\)
\(=\frac{k^4+2k^2\left(k+1\right)+\left(k+1\right)^2}{k^2\left(k+1\right)^2}=\frac{\left(k^2+k+1\right)^2}{\left(k\left(k+1\right)\right)^2}\)
\(\Rightarrow\sqrt{1+\frac{1}{k^2}+\frac{1}{\left(k+1\right)^2}}=\frac{k^2+k+1}{k^2+k}=1+\frac{1}{k\left(k+1\right)}=1+\frac{1}{k}-\frac{1}{k+1}\)
\(\Rightarrow S=1+1-\frac{1}{2}+1+\frac{1}{2}-\frac{1}{3}+1+\frac{1}{3}-\frac{1}{4}+...+1+\frac{1}{2013}-\frac{1}{2014}=2014-\frac{1}{2014}\)
Mỗi biểu thức trong dấu căn có dạng:
1+1k2 +1(k+1)2 ( Với k≥2)
Ta có:
1+1k2 +1(k+1)2 =k2(k+1)2+(k+1)2+k2k2(k+1)2 =k4+2k3+k2+k2+2k+1+k2k2(k+1)2
=k4+2k2(k+1)+(k+1)2k2(k+1)2 =(k2+k+1)2(k(k+1))2
⇒√1+1k2 +1(k+1)2 =k2+k+1k2+k =1+1k(k+1) =1+1k −1k+1
⇒S=1+1−12 +1+12 −13 +1+13 −14 +...+1+12013 −12014 =2014−12014
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
ĐK : \(\hept{\begin{cases}x\ge2013\\y\ge2014\end{cases}}\)
Ta có \(A=\frac{\sqrt{\left(x-2013\right).2015}}{\sqrt{2015}\left(x+2\right)}+\frac{\sqrt{\left(x-2014\right).2014}}{\sqrt{2014}.x}\le\frac{\frac{x-2013+2015}{2}}{\sqrt{2015}\left(x+2\right)}+\frac{\frac{x-2014+2014}{2}}{\sqrt{2014}.x}\)
\(\Rightarrow A\le\frac{1}{2\sqrt{2015}}+\frac{1}{2\sqrt{2014}}\)
Vậy .............................................
![](https://rs.olm.vn/images/avt/0.png?1311)
* Cách 1:
\(\sqrt{1^2+2013^2+\frac{2013^2}{2014^2}}\)
\(=\sqrt{2013^2.\left(1+\frac{1}{2013^2}+\frac{1}{2014^2}\right)}\)
\(=2013.\left(1+\frac{1}{2013}-\frac{1}{2014}\right)\)
\(=2013+1-\frac{2013}{2014}\)
\(=2014-\frac{2013}{2014}\)
* Cách 2:
\(\sqrt{1^2+2013^2+\frac{2013^2}{2014^2}}\)
\(=\sqrt{\left(1+2013\right)^2-2.2013+\frac{2013^2}{2014^2}}\)
\(=\sqrt{2014^2-2.2013+\left(\frac{2013}{2014}\right)^2}\)
\(=\sqrt{\left(2014-\frac{2013}{2014}\right)^2}\)
\(=2014-\frac{2013}{2014}\)
Từ 2 cách trên ta suy ra:
\(\sqrt{1^2+2013^2+\frac{2013^2}{2014^2}}+\frac{2013}{2014}\)
\(=2014-\frac{2013}{2014}+\frac{2013}{2014}\)
\(=2014\)
Theo đề bài trên, ta có thể suy ra công thức tổng quát như sau:
\(\sqrt{1^2+x^2+\frac{x^2}{\left(x+1\right)^2}}+\frac{x}{x+1}\)
(Chúc bạn học tốt và nhớ k cho mình với nhá!)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta cần chứng minh:
\(\frac{2014}{\sqrt{2013}}+\frac{2013}{\sqrt{2014}}>\sqrt{2013}+\sqrt{2014}\)
\(\Leftrightarrow\frac{\sqrt{2013^3}+\sqrt{2014^3}}{\sqrt{2013}.\sqrt{2014}}>\sqrt{2013}+\sqrt{2014}\)
\(\Leftrightarrow\frac{\left(\sqrt{2013}+\sqrt{2014}\right)\left(2013-\sqrt{2013}.\sqrt{2014}+2014\right)}{\sqrt{2013}.\sqrt{2014}}>\sqrt{2013}+\sqrt{2014}\)
\(\Leftrightarrow\frac{2013-\sqrt{2013}.\sqrt{2014}+2014}{\sqrt{2013}.\sqrt{2014}}>1\)
\(\Leftrightarrow2013-2\sqrt{2013}.\sqrt{2014}+2014>0\)
\(\Leftrightarrow\left(\sqrt{2013}-\sqrt{2014}\right)^2>0\)đúng
![](https://rs.olm.vn/images/avt/0.png?1311)
\(P\left(x\right)=\frac{2012x+2013\sqrt{1-x^2}+2014}{\sqrt{1-x^2}}=\frac{2012x+2014}{\sqrt{1-x^2}}+\frac{2013\sqrt{1-x^2}}{\sqrt{1-x^2}}\)
\(=\frac{2012x+2014}{\sqrt{1-x^2}}+2013=2012+\frac{2012\left(1+x\right)+1-x}{\sqrt{1-x^2}}\)
Áp dụng BĐT AM-GM ta có:
\(P\left(x\right)\ge2012+\frac{2\sqrt{2012\left(1+x\right)\left(1-x\right)}}{\sqrt{1-x^2}}=2012+2\sqrt{2012}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
=\(2013\) \(+\frac{2014+2012x}{\sqrt{1-x^2}}\) =\(\frac{2013\left(1+x\right)+1-x}{\sqrt{1-x^2}}\) \(\ge2013+\frac{2\sqrt{2013\left(1+x\right)\left(1-x\right)}}{\sqrt{1-x^2}}=2013+2\sqrt{2013}\)
dau = xay ra khi \(2013\left(1+x\right)=1-x\)
\(\Leftrightarrow x=-\frac{1001}{1002}\)
min p(x) =\(2013+2\sqrt{2013}\Leftrightarrow x=-\frac{1001}{1002}\)