\(A=\frac{5-\sqrt{5}}{\sqrt{5}-1}=\frac{5\sqrt{5}+5-5-\sqrt{5}}{\sqrt{5^2}-1}=\frac{5\sqrt{5}-\sqrt{5}}{5-1}=\frac{4\sqrt{5}}{4}=\sqrt{5}\)

Vì hai vế đều dương nên bình phương hai vế, ta được:

\(H^2=\left(\sqrt{x+2\sqrt{2x-4}}+\sqrt{x-2\sqrt{2x-4}}\right)^2\)

      \(=x+2\sqrt{2x-4}+x-2\sqrt{2x-4}+2\sqrt{\left(x+2\sqrt{2x-4}\right)\left(x-2\sqrt{2x-4}\right)}\)

        \(=2x+2\sqrt{x^2-4\left(2x-4\right)}=2x+2\sqrt{x^2-8x+16}\)

         =2x + 2√ (x-4)^2 = 2x + 2|x-4|

Đến đây bạn tự làm tiếp nha (với x>2)

đk : x ≥ 2 
Bạn bình phương 2 vế, thu gọn đc: 
3√[x(x−2)(x+1)] ≤ 2x2−6x−2 
<=> 3√[(x2−2x)(x+1)] ≤ 2(x2−2x) − 2(x+1) 
Chia 2 vế cho (x+1), đặt t= căn((x2−2x)/(x+1)), t≥ 0 ta đc: 
2t^2 - 3t - 2 ≥ 0 => t ≥ 2 
<=> x^2 - 2x ≥ 4x + 4 
<=> x^2 - 6x -4 ≥ 0 
<=> x ≥ 3+√13

P/s: Tham khảo nhé

\(\sqrt{x+2\sqrt{x-4}}+\sqrt{x-2\sqrt{2x-4}}\)

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

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

\(=\sqrt{x+2.\left|\sqrt{x}-2\right|}+\sqrt{x-2.\left|\sqrt{2x}-2\right|}\)

\(=\sqrt{x+2.\left(\sqrt{x}-2\right)}+\sqrt{x-2.\left(\sqrt{2x}-2\right)}\)

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

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

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

\(=2x+2\sqrt{x}-2\sqrt{2x}\)

\(=2x+2\sqrt{x}-2\sqrt{2}.\sqrt{x}\)

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

ĐKXĐ: \(x\ge2\)

\(A=\sqrt{x+2\sqrt{2x-4}}+\sqrt{x-2\sqrt{2x-4}}\)

\(=\sqrt{x-2+2.\sqrt{x-2}.\sqrt{2}+2}+\sqrt{x-2-2.\sqrt{x-2}.\sqrt{2}+2}\)

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

\(=\left|\sqrt{x-2}+\sqrt{2}\right|+\left|\sqrt{x-2}-\sqrt{2}\right|=\sqrt{x-2}+\sqrt{2}+\left|\sqrt{x-2}-\sqrt{2}\right|\)

Xét \(x\ge4\Rightarrow\sqrt{x-2}\ge\sqrt{2}\)

\(\Rightarrow A=\sqrt{x-2}+\sqrt{2}+\sqrt{x-2}-\sqrt{2}=2\sqrt{x-2}\)

Xét \(0\le x< 4\Rightarrow\sqrt{x-2}< \sqrt{2}\)

\(\Rightarrow A=\sqrt{x-2}+\sqrt{2}-\sqrt{x-2}+\sqrt{2}=2\sqrt{2}\)

\(\sqrt{2x+2\sqrt{x^2-4}}\)

\(\sqrt{x-2+2\sqrt{x-2}\sqrt{x+2}+x+2}\)\(\)

\(\sqrt{\left(\sqrt{x-2}+\sqrt{x+2}\right)^2}\)

\(\left|\sqrt{x-2}\right|+\left|\sqrt{x+2}\right|\)

\(\sqrt{x-2}+\sqrt{x+2}\)

\(=\sqrt{7}\)

Sửa đề: x-4

\(A=\dfrac{x-2\sqrt{x}+x+4\sqrt{x}+4+2x+8}{x-4}=\dfrac{4x+2\sqrt{x}+12}{x-4}\)

a) \(3\sqrt{2x}-4\sqrt{2x}+8-2\sqrt{x}\)

\(=-\left(4\sqrt{2x}-3\sqrt{2x}\right)+8-2\sqrt{x}\)

\(=-\sqrt{2x}-2\sqrt{x}+8\) 

b) \(3\sqrt{2x}-\sqrt{72x}+3\sqrt{18x}+18\)

\(=3\sqrt{2x}-6\sqrt{2x}+3\cdot3\sqrt{2x}+18\)

\(=3\sqrt{2x}-6\sqrt{2x}+9\sqrt{2x}+18\)

\(=\left(3+9-6\right)\sqrt{2x}+18\)

\(=6\sqrt{2x}+18\)