1.[tex]\frac{2x^2+1}{\sqrt{4x^2-1}}=\frac{2x^2+1}{\sqrt{2x^2+1}.\sqrt{2x^2-1}}=\frac{\sqrt{2x^2+1}}{\sqrt{2x^2-1}}=\sqrt{\frac{2x^2+1}{2x^2-1}}>1[/tex]
2. [tex]\frac{3}{4}A=\frac{3}{4x-4\sqrt{x}+4}=\frac{3}{(2\sqrt{x}-1)^2+3}\leq \frac{3}{3}=1\Rightarrow A\leq \frac{4}{3}[/tex]
Dấu "=" xảy ra khi [tex]x=\frac{1}{4 }[/tex]