\(\sqrt{2006+2\sqrt{2005}}-\sqrt{2006-2\sqrt{2005}}\)

\(=\sqrt{\left(\sqrt{2005}+1\right)^2}-\sqrt{\left(\sqrt{2005}-1\right)^2}\)

\(=\left(\sqrt{2005}+1\right)-\left(\sqrt{2005}-1\right)\)

= 2

M = \(\sqrt{4-\sqrt{7}}-\sqrt{4+\sqrt{7}}\)

\(\Rightarrow\sqrt{2}M\)\(=\sqrt{8-2\sqrt{7}}-\sqrt{8+2\sqrt{7}}\)

\(=\sqrt{\left(\sqrt{7}-1\right)^2}-\sqrt{\left(\sqrt{7}+1\right)^2}\)

\(=\left(\sqrt{7}-1\right)-\left(\sqrt{7}+1\right)\)

= - 2

\(\Rightarrow M=-\sqrt{2}\)

Áp dụng BĐT \(\dfrac{1}{x+y}\le\dfrac{1}{4}\left(\dfrac{1}{x}+\dfrac{1}{y}\right)\), ta có:

\(\dfrac{4}{2a+b+c}+\dfrac{4}{a+2b+c}+\dfrac{4}{a+b+2c}\)

\(\le\dfrac{1}{4}\left(\dfrac{4}{a+b}+\dfrac{4}{a+c}+\dfrac{4}{a+b}+\dfrac{4}{c+b}+\dfrac{4}{a+c}+\dfrac{4}{b+c}\right)\)

\(=\dfrac{2}{a+b}+\dfrac{2}{a+c}+\dfrac{2}{b+c}\)

\(\le\dfrac{1}{4}\left(\dfrac{2}{a}+\dfrac{2}{b}+\dfrac{2}{a}+\dfrac{2}{c}+\dfrac{2}{b}+\dfrac{2}{c}\right)\)

\(=\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}\left(\text{đ}pcm\right)\)

Dấu "=" xảy ra khi a = b = c

\(\dfrac{x\sqrt{x}-y\sqrt{y}}{x+\sqrt{xy}+y}\)

\(=\dfrac{\left(\sqrt{x}-\sqrt{y}\right)\left(x+\sqrt{xy}+y\right)}{x+\sqrt{xy}+y}\)

\(=\sqrt{x}-\sqrt{y}\)

\(\dfrac{2+\sqrt{3}}{\sqrt{2}+\sqrt{2+\sqrt{3}}}+\dfrac{2-\sqrt{3}}{\sqrt{2}-\sqrt{2-\sqrt{3}}}\)

\(=\dfrac{\left(2+\sqrt{3}\right)\left(\sqrt{2}-\sqrt{2-\sqrt{3}}\right)+\left(2-\sqrt{3}\right)\left(\sqrt{2}+\sqrt{2+\sqrt{3}}\right)}{\left(\sqrt{2}+\sqrt{2+\sqrt{3}}\right)\left(\sqrt{2}-\sqrt{2-\sqrt{3}}\right)}\)

\(\left[-\text{tử}-\right]=\sqrt{2}\left(2+\sqrt{3}\right)-\sqrt{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)^2}+\sqrt{2}\left(2-\sqrt{3}\right)+\sqrt{\left(2+\sqrt{3}\right)\left(2-\sqrt{3}\right)^2}\)

\(=4\sqrt{2}-\sqrt{2+\sqrt{3}}+\sqrt{2-\sqrt{3}}\)

\(\left[-\text{mẫu}-\right]=2-\sqrt{4-2\sqrt{3}}+\sqrt{4+2\sqrt{3}}-\sqrt{\left(2+\sqrt{3}\right)\left(2-\sqrt{3}\right)}\)

\(=2-\sqrt{\left(\sqrt{3}-1\right)^2}+\sqrt{\left(\sqrt{3}+1\right)^2}-\sqrt{4-3}\)

\(=2-\left(\sqrt{3}-1\right)+\left(\sqrt{3}+1\right)-1\)

= 3

Ta có:

\(\dfrac{4\sqrt{2}-\sqrt{2+\sqrt{3}}+\sqrt{2-\sqrt{3}}}{3}\)

\(=\dfrac{8-\sqrt{4+2\sqrt{3}}+\sqrt{4-2\sqrt{3}}}{3\sqrt{2}}\)

\(=\dfrac{8-\sqrt{\left(\sqrt{3}+1\right)^2}+\sqrt{\left(\sqrt{3}-1\right)^2}}{3\sqrt{2}}\)

\(=\dfrac{8-\left(\sqrt{3}+1\right)+\left(\sqrt{3}-1\right)}{3\sqrt{2}}=\dfrac{6}{3\sqrt{2}}=\sqrt{2}\)

\(\sqrt{\dfrac{2+a-2\sqrt{2a}}{a+3-2\sqrt{3a}}}\)

\(=\sqrt{\dfrac{\left(\sqrt{a}-\sqrt{2}\right)^2}{\left(\sqrt{a}-\sqrt{3}\right)^2}}\)

\(=\dfrac{\left|\sqrt{a}-\sqrt{2}\right|}{\left|\sqrt{a}-\sqrt{3}\right|}\)

\(\dfrac{\sqrt{14-6\sqrt{5}}}{\sqrt{5}-3}\)

\(=\dfrac{\sqrt{\left(3-\sqrt{5}\right)^2}}{\sqrt{5}-3}\)

\(=\dfrac{3-\sqrt{5}}{\sqrt{5}-3}\)

= - 1

\(\dfrac{\sqrt{3+\sqrt{5}}}{\sqrt{2}}\)

\(=\dfrac{\sqrt{6+2\sqrt{5}}}{2}\)

\(=\dfrac{\sqrt{\left(\sqrt{5}+1\right)^2}}{2}\)

\(=\dfrac{\sqrt{5}+1}{2}\)

\(\dfrac{2+\sqrt{2}}{\sqrt{1,5+\sqrt{2}}}\)

\(=\dfrac{2\sqrt{2}+2}{\sqrt{3+2\sqrt{2}}}\)

\(=\dfrac{2\left(\sqrt{2}+1\right)}{\sqrt{\left(\sqrt{2}+1\right)^2}}\)

\(=\dfrac{2\left(\sqrt{2}+1\right)}{\sqrt{2}+1}\)

= 2

\(\dfrac{\sqrt{20}}{\sqrt{5}}+\dfrac{\sqrt{117}}{\sqrt{13}}+\dfrac{\sqrt{272}}{\sqrt{17}}+\dfrac{\sqrt{105}}{\sqrt{2\dfrac{1}{7}}}\)

\(=4+9+16+49\)

= 78

\(M=\dfrac{2x+1}{x^2}\)

\(=\dfrac{-x^2+\left(x^2+2x+1\right)}{x^2}\)

\(=-1+\dfrac{\left(x+1\right)^2}{x^2}\ge-1\)

Dấu "=" xảy ra khi x = - 1

\(M=\dfrac{4x^2-2x+1}{x^2}\)

\(=\dfrac{3x^2+\left(x^2-2x+1\right)}{x^2}\)

\(=3+\dfrac{\left(x-1\right)^2}{x^2}\ge3\)

Dấu "=" xảy ra khi x = 1

\(\dfrac{1}{\sqrt{2}-\sqrt{3}}\times\sqrt{\dfrac{3\sqrt{2}-2\sqrt{3}}{3\sqrt{2}+2\sqrt{3}}}\)

\(=\dfrac{\sqrt{2}+\sqrt{3}}{2-3}\times\sqrt{\dfrac{\left(3\sqrt{2}-2\sqrt{3}\right)^2}{18-12}}\)

\(=-\left(\sqrt{3}+\sqrt{2}\right)\times\dfrac{\sqrt{2}\times\sqrt{3}\times\left(\sqrt{3}-\sqrt{2}\right)}{\sqrt{6}}\)

\(=-\left(3-2\right)\)

= - 1

ko phân tích đc ~~ 

~ ~ ~ Áp dụng đẳng thức \(\left(a+b\right)^2+\left(a-b\right)^2=2\left(a^2+b^2\right)\) ~ ~ ~

a)

\(\left(\sin\alpha+\cos\alpha\right)^2-2\sin\alpha\cos\alpha-1\)

\(=\left(\sin\alpha+\cos\alpha\right)^2-\left(2\sin\alpha\cos\alpha+\sin^2\alpha+\cos^2\alpha\right)\)

\(=\left(\sin\alpha+\cos\alpha\right)^2-\left(\sin\alpha+\cos\alpha\right)^2\)

= 0

b)

\(\left(\sin\alpha-\cos\alpha\right)^2+2\sin\alpha\cos\alpha+1\)

\(=\left(\sin\alpha-\cos\alpha\right)^2+2\sin\alpha\cos\alpha+\sin^2\alpha+\cos^2\alpha\)

\(=\left(\sin\alpha-\cos\alpha\right)^2+\left(\sin\alpha+\cos\alpha\right)^2\)

\(=2\left(\sin^2\alpha+\cos^2\alpha\right)\)

= 2

c)

\(\left(\sin\alpha+\cos\alpha\right)^2+\left(\sin\alpha-\cos\alpha\right)^2+2\)

\(=2\left(\sin^2\alpha+\cos^2\alpha\right)+2\)

= 4

d)

\(\sin^2\alpha\cot^2\alpha+\cos^2\alpha\tan^2\alpha\)

\(=\left(\sin\times\dfrac{\cos}{\sin}\right)^2+\left(\cos\times\dfrac{\sin}{\cos}\right)^2\)

= 1

1234 + 1243 + 1324 + 1342 + 1432 + 1423 + 2314 + 2341 + 2143 + 2134 + 2431 + 2413 + 3214 + 3241 + 3412 + 3421 + 3124 + 3142 + 4321 + 4312 + 4132 + 4123 + 4213 + 4231 = 66660

\(\sqrt{49-5\sqrt{96}}-\sqrt{49+5\sqrt{96}}\)

\(=\sqrt{49-20\sqrt{6}}-\sqrt{49+20\sqrt{6}}\)

\(=\sqrt{\left(5-2\sqrt{6}\right)^2}-\sqrt{\left(5+2\sqrt{6}\right)^2}\)

\(=\left(5-2\sqrt{6}\right)-\left(5+2\sqrt{6}\right)\)

\(=-4\sqrt{6}\)