+ Theo BĐT AM - GM :
\(2P=2x+\frac{4}{2x+1}=2x+1+\frac{4}{2x+1}-1\)
\(\ge2\sqrt{\left(2x+1\right)\cdot\frac{4}{2x+1}}-1=3\) \(\Rightarrow P\ge\frac{3}{2}\)
Dấu "=" \(\Leftrightarrow2x+1=\frac{4}{2x+1}\Leftrightarrow x=\frac{1}{2}\)
Vậy Min \(P=\frac{3}{2}\Leftrightarrow x=\frac{1}{2}\)