Mình ko rõ đề bài 

\(y=\frac{3x}{2}+\frac{1}{x}+1\)hay \(y=\frac{3x}{2}+\frac{1}{x+1}\)

\(y=\frac{x}{1-x}+\frac{5}{x}=\frac{x}{1-x}+\frac{5\left(1-x\right)}{x}+5\)

Áp dụng BĐT Cô - si ta có :

\(\frac{x}{1-x}+\frac{5\left(1-x\right)}{x}\ge2\sqrt{\frac{5x\left(1-x\right)}{x\left(1-x\right)}}=2\sqrt{5}\)

\(\Rightarrow y\ge5+2\sqrt{5}\)

Dấu \("="\) xảy ra khi \(x^2=5x^2-10x+5\Leftrightarrow4x^2-10x+5=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x_1=\frac{5+\sqrt{5}}{4}\\x_2=\frac{5-\sqrt{5}}{4}\end{matrix}\right.\)

\(y=\frac{x}{3}+\frac{5}{2x-1}=\frac{2x}{6}+\frac{5}{2x-1}=\frac{2x-1}{6}+\frac{5}{2x-1}+\frac{1}{6}\)

\(\Rightarrow y\ge2\sqrt{\frac{2x-1}{6}.\frac{5}{2x-1}}+\frac{1}{6}=\frac{\sqrt{30}}{3}+\frac{1}{6}\)

\(\Rightarrow P_{min}=\frac{\sqrt{30}}{3}+\frac{1}{6}\)

Dấu "=" xảy ra khi \(\left(2x-1\right)^2=30\Rightarrow x=\frac{\sqrt{30}+1}{2}\)

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

\(\Rightarrow y\ge2\sqrt{\frac{3\left(x+1\right)}{2}.\frac{1}{x+1}}-\frac{3}{2}=\sqrt{6}-\frac{3}{2}\)

Dấu "=" khi \(\left(x+1\right)^2=\frac{2}{3}\Rightarrow x=\frac{\sqrt{6}}{3}-1\)

Do \(x+3\) và \(5-2x\) đều không âm, áp dụng BĐT \(ab\le\frac{\left(a+b\right)^2}{4}\) ta có

\(y=\frac{1}{2}.\left(2x+6\right)\left(5-2x\right)\le\frac{1}{2}.\frac{\left(2x+6+5-2x\right)^2}{4}=\frac{1}{2}.\frac{11^2}{4}=\frac{121}{8}\)

\(\Rightarrow y_{max}=\frac{121}{8}\) khi \(2x+6=5-2x\Leftrightarrow x=\frac{-1}{4}\)

\(đkcđ\Leftrightarrow x\ge0\)

\(B=\frac{x+5}{\sqrt{x}+2}=\frac{x-4+9}{\sqrt{x}+2}=\frac{x-4}{\sqrt{x}+2}+\frac{9}{\sqrt{x}+2}.\)

\(=\frac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}{\sqrt{x}+2}+\frac{9}{\sqrt{x}+2}=\sqrt{x}-2+\frac{9}{\sqrt{x}+2}\)

\(=\sqrt{x}+2+\frac{9}{\sqrt{x}+2}-4\)

Áp dụng bđt Cô - si cho hai số dương \(\sqrt{x}+2\)và \(\frac{9}{\sqrt{x}+2}\), ta có :

\(\sqrt{x}+2+\frac{9}{\sqrt{x}+2}\ge2\sqrt{\frac{\left(\sqrt{x}+2\right).9}{\sqrt{x}+2}}\)

\(\Rightarrow\sqrt{x}+2+\frac{9}{\sqrt{x}+2}\ge2.3\)

\(\Rightarrow\sqrt{x}+2+\frac{9}{\sqrt{x}+2}-4\ge6-4\)

\(\Rightarrow\sqrt{x}+2+\frac{9}{\sqrt{x}+2}-4\ge2\)

Hay \(B_{min}=2\)\(\Leftrightarrow\sqrt{x}+2=\frac{9}{\sqrt{x}+2}\)

\(\Rightarrow\sqrt{x}+2-\frac{9}{\sqrt{x}+2}=0\)

\(\Rightarrow\frac{\left(\sqrt{x}+2\right)^2-9}{\sqrt{x}+2}=0\)

\(\Rightarrow\left(\sqrt{x}+2\right)^2-3^2=0\)

\(\Rightarrow\left(\sqrt{x}+2-3\right)\left(\sqrt{x}+2+3\right)=0\)

\(\Rightarrow\left(\sqrt{x}-1\right)\left(\sqrt{x}+5\right)=0\)

Vì \(\sqrt{x}+5>0\Rightarrow\sqrt{x}-1=0\)

\(\Rightarrow\sqrt{x}=1\Rightarrow x=1\)

\(KL:B_{min}=2\Leftrightarrow x=1\)