\(M=\frac{3\sqrt{x}-2}{\sqrt{x}+2}=\frac{3\left(\sqrt{x}+2\right)-8}{\sqrt{x}+2}=1-\frac{8}{\sqrt{x}+2}\ge1\)

Min M = 1 \(\Leftrightarrow\frac{8}{\sqrt{x}+2}=0\left(1\right)\)

Mà \(\hept{\begin{cases}8>0\\\sqrt{x}+2>0\forall x\end{cases}\Leftrightarrow\frac{8}{\sqrt{x}+2}>0\left(2\right)}\)

Từ ( 1 ) và ( 2 ) => Không tìm được GTNN của M thỏa mãn  \(M=\frac{3\sqrt{x}-2}{\sqrt{x}+2}\)

               Bài làm :

\(a\text{)}\sqrt{x-3}=5\Leftrightarrow\sqrt{x-3}=\sqrt{25}\Leftrightarrow x-3=25\Leftrightarrow x=28\)

\(b\text{)}\sqrt{3x}=3\sqrt{5}\Leftrightarrow\sqrt{3x}=\sqrt{9}.\sqrt{5}\Leftrightarrow\sqrt{3x}=\sqrt{45}\Leftrightarrow3x=45\Leftrightarrow x=\frac{45}{3}=15\)

\(c\text{)}\sqrt{x^2+2x+1}=10\Leftrightarrow\sqrt{\left(x+1\right)^2}=\sqrt{100}\Leftrightarrow\left(x+1\right)^2=10\Leftrightarrow\orbr{\begin{cases}x+1=10\\x+1=-10\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=9\\x=-11\end{cases}}\)

a) \(ĐKXĐ:x\ge3\)

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

\(\Leftrightarrow x-3=25\) \(\Leftrightarrow x=28\)( thỏa mãn )

Vậy \(x=28\)

b) \(ĐKXĐ:x\ge0\)

\(\sqrt{3x}=3\sqrt{5}\)\(\Leftrightarrow\left(\sqrt{3x}\right)^2=\left(3\sqrt{5}\right)^2\)

\(\Leftrightarrow3x=45\)\(\Leftrightarrow x=15\)( thỏa mãn )

Vậy \(x=15\)

c) \(ĐKXĐ:x\inℝ\)

\(\sqrt{x^2+2x+1}=10\)\(\Leftrightarrow\sqrt{\left(x+1\right)^2}=10\)

\(\Leftrightarrow\left|x+1\right|=10\)\(\Leftrightarrow\orbr{\begin{cases}x+1=-10\\x+1=10\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-11\\x=9\end{cases}}\)( thỏa mãn )

Vậy \(x=-11\)hoặc \(x=9\)

Check lại đề đi bạn ơi! Chứng minh \(\frac{1}{1+x^2}+\frac{1}{1+y^2}\ge\frac{2}{1+xy}\) thì được

\(A=\frac{x^2+2x+3}{x^2+4x+4}-\frac{2}{3}+\frac{2}{3}\)

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

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

\(\hept{\begin{cases}\left(x-1\right)^2\ge0\\\left(x+2\right)^2\ge0\end{cases}\Rightarrow\frac{\left(x-1\right)^2}{\left(x+2\right)^2}\ge0}\)

Dấu '' ='' xảy ra khi và chỉ khi  x=1

=> Min A =2/3 khi x=1

ĐK: \(x\ge0;x\ne1\)

Ta có: \(P=\text{[}\frac{\sqrt{x}-2}{x-1}-\frac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}\text{]}\left(\frac{1-x}{\sqrt{2}}\right)^2\)

\(=\text{[}\frac{\sqrt{x}-2}{x-1}-\frac{x+\sqrt{x}-2}{\left(x-1\right)\left(\sqrt{x}+1\right)}\text{]}\frac{\left(x-1\right)^2}{2}\)

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

\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)-\left(x+\sqrt{x}-2\right)}{\sqrt{x}+1}.\frac{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}{2}\)

\(-2\sqrt{x}.\frac{\sqrt{x}-1}{2}\)\(=\sqrt{x}-x\)

Ta có \(x^2-x-1=0\Rightarrow x^2-x=1\Rightarrow\left(x^2-x\right)^3=1\)

\(\Rightarrow x^6-3x^5+3x^4-x^3=1\)

Mặt khác \(x^2-x-1-0\Rightarrow x^2=x+1\)

\(\Rightarrow x^6=\left(x+1\right)^3=x^3+2=3x^2+3x+1\)

\(\Rightarrow P=\frac{1+2017}{1+2017}=1\)