So sánh:
a) \(A=\sqrt{2012}-\sqrt{2011}\) ; \(B=\sqrt{2013}-\sqrt{2012}\)
\(A=\frac{2011}{\sqrt{2012}}+\frac{2012}{\sqrt{2011}};B=\sqrt{2011}+\sqrt{2012}.\)
So sánh A và B
so sánh A và B biết \(A=\dfrac{2011}{\sqrt{2012}}+\dfrac{2012}{\sqrt{2011}}vàB=\sqrt{2011}+\sqrt{2012}\)
Đặt \(\sqrt{2011}=a;\sqrt{2012}=b\)
Theo đề, ta có: \(A=\dfrac{a^2}{b}+\dfrac{b^2}{a}=\dfrac{a^3+b^3}{ab}\)
B=a+b
\(A-B=\dfrac{a^3+b^3}{ab}-\left(a+b\right)=\dfrac{a^3+b^3-a^2b-ab^2}{ab}\)
\(=\dfrac{\left(a+b\right)\left(a^2-ab+b^2\right)-ab\left(a+b\right)}{ab}\)
\(=\dfrac{\left(a+b\right)\left(a-b\right)^2}{ab}>0\)
=>A>B
New: So sánh hai tổng A và B nếu:
\(A=\frac{2011}{\sqrt{2012}}+\frac{2012}{\sqrt{2011}}\) và \(B=\sqrt{2011}+\sqrt{2012}\)
A = \(\frac{2012-1}{\sqrt{2012}}+\frac{2011+1}{\sqrt{2011}}=\sqrt{2012}-\frac{1}{\sqrt{2012}}+\sqrt{2011}+\frac{1}{\sqrt{2011}}\)
A = \(\sqrt{2012}+\sqrt{2011}+\left(\frac{1}{\sqrt{2011}}-\frac{1}{\sqrt{2012}}\right)=B+\left(\frac{1}{\sqrt{2011}}-\frac{1}{\sqrt{2012}}\right)\)
Mà 2011 < 2012 nên \(\frac{1}{\sqrt{2011}}>\frac{1}{\sqrt{2012}}\Rightarrow\frac{1}{\sqrt{2011}}-\frac{1}{\sqrt{2012}}>0\)
=> A > B
cho A và B hãy so sánh
\(A=\sqrt{2012}-\sqrt{2011};B=\sqrt{2013}-\sqrt{2012}\)
A) SO SÁNH \(\sqrt{2013}-\sqrt{2010}\) và \(\sqrt{2012}-\sqrt{2011}\)
B) SO SÁNH \(\frac{2013}{\sqrt{2012}}+\frac{2012}{\sqrt{2013}}\)và \(\sqrt{2013}+\sqrt{2012}\)
A) SO SÁNH \(\sqrt{2013}-\sqrt{2010}\) và \(\sqrt{2012}-\sqrt{2011}\)
B) SO SÁNH\(\frac{2013}{\sqrt{2012}}+\frac{2012}{\sqrt{2013}}\)và \(\sqrt{2013}+\sqrt{2012}\)
THANKS
so sánh \(\sqrt{2013}-\sqrt{2012}\) và \(\sqrt{2012}-\sqrt{2011}\)
giúp mình!!!!!!!!!!!1
Các số thực x, y, z thỏa mãn:
\(\hept{\begin{cases}\sqrt{x+2011}+\sqrt{y+2012}+\sqrt{z+2013}=\sqrt{y+2011}+\sqrt{z+2012}+\sqrt{x+2013}\\\sqrt{y+2011}+\sqrt{z+2012}+\sqrt{x+2013}=\sqrt{z+2011}+\sqrt{x+2012}+\sqrt{y+2013}\end{cases}}\)
CMR: \(x=y=z\)
Đặt \(\hept{\begin{cases}a=x+2011\\b=y+2011\\c=z+2011\end{cases}}\) Ta có Hệ:
\(\hept{\begin{cases}\sqrt{a}+\sqrt{b+1}+\sqrt{c+2}\left(A\right)=\sqrt{b}+\sqrt{c+1}+\sqrt{a+2}\left(B\right)\\\sqrt{b}+\sqrt{c+1}+\sqrt{a+2}\left(B\right)=\sqrt{c}+\sqrt{a+1}+\sqrt{b+2}\left(C\right)\end{cases}}\)
Vai trò \(x,y,z\) bình đẳng
Giả sử \(c=Max\left(a;b;c\right)\) vì \(A=C\) ta có:
\(\sqrt{a}+\sqrt{b+1}+\sqrt{c+2}=\sqrt{c}+\sqrt{a+1}+\sqrt{b+2}\)
\(\Leftrightarrow\left(\sqrt{a+1}-\sqrt{a}\right)+\left(\sqrt{b+2}-\sqrt{b+1}\right)\)
\(=\sqrt{c+2}-\sqrt{c}=\left(\sqrt{c+2}-\sqrt{c+1}\right)+\left(\sqrt{c+1}-\sqrt{c}\right)\)
\(\Leftrightarrow\frac{1}{\sqrt{a+1}+\sqrt{a}}+\frac{1}{\sqrt{b+2}+\sqrt{b+1}}\)
\(=\frac{1}{\sqrt{c+2}+\sqrt{c+1}}+\frac{1}{\sqrt{c+1}+\sqrt{c}}\left(1\right)\)
Mặt khác \(\hept{\begin{cases}c\ge a\Rightarrow\frac{1}{\sqrt{a+1}+\sqrt{a}}\le\frac{1}{\sqrt{c+1}+\sqrt{c}}\\c\ge b\Rightarrow\frac{1}{\sqrt{b+2}+\sqrt{b+1}}\le\frac{1}{\sqrt{c+2}+\sqrt{c+1}}\end{cases}}\)
Suy ra \(\left(1\right)\) xảy ra khi \(a=b=c\Leftrightarrow x=y=z\) (Đpcm)
So sánh bằng cách bình phương hai vế:
\(\sqrt{2012}-\sqrt{2011}\)và \(\sqrt{2011}-\sqrt{2010}\)
Chưa tính nhưg nghĩ là
\(\sqrt{2012}-\sqrt{2011}\) > \(\sqrt{2011}-\sqrt{2010}\)