Ta có: \(A^2=4026+2\cdot\sqrt{2012\cdot2014}\)

\(B^2=4026+4026=4026+2\cdot\sqrt{2013^2}\)

mà \(2012\cdot2014< 2013^2\)

nên A<B

2 căn 2012 lớn hơn căn 2012 + căn 2014

\(\left(\sqrt{2013}+\sqrt{2015}\right)^2=2013+2015+2\sqrt{2013.2015}=4028+2\sqrt{2013.2015}\)

\(\left(2\sqrt{2014}\right)^2=4.2014=4028+2\sqrt{2014^2}\)

Ta có: \(2013.2015=2014^2-1< 2014^2\)

Do đó \(\sqrt{2013}+\sqrt{2015}< 2\sqrt{2014}\)

Lời giải:

Hiển nhiên $\sqrt{2011}> \sqrt{2010}$

$\sqrt{2009}>0$

$\Rightarrow \sqrt{2009}+\sqrt{2011}> \sqrt{2010}$

Bài 2:

a: ĐKXĐ: x>=0

\(\sqrt{3x}-5\sqrt{12x}+7\cdot\sqrt{27x}=12\)

=>\(\sqrt{3x}-5\cdot2\sqrt{3x}+7\cdot3\sqrt{3x}=12\)

=>\(12\sqrt{3x}=12\)

=>\(\sqrt{3x}=1\)

=>3x=1

=>x=1/3(nhận)

Bài 1:

a: \(A=\left(\sqrt{\frac23}+\sqrt{\frac{50}{3}}-\sqrt{24}\right)\cdot\sqrt6\)

\(=\left(\frac{2\sqrt6}{6}+\sqrt{\frac{100}{6}}-2\sqrt6\right)\cdot\sqrt6\)

\(=2+\sqrt{100}-2\cdot6=2+10-12=0\)

b: \(B=\left(\frac{\sqrt{14}-\sqrt7}{\sqrt2-1}+\frac{\sqrt{15}-\sqrt5}{\sqrt3-1}\right):\frac{1}{\sqrt7-\sqrt5}\)

\(=\left(\frac{\sqrt7\left(\sqrt2-1\right)}{\sqrt2-1}+\frac{\sqrt5\left(\sqrt3-1\right)}{\sqrt3-1}\right)\cdot\left(\sqrt7-\sqrt5\right)\)

\(=\left(\sqrt7+\sqrt5\right)\left(\sqrt7-\sqrt5\right)\)

=7-5

=2

cmr là cái j

Lê Thanh Thùy Ngân 

cmr là chứng minh rằng bạn nhé