Đkxđ x>0
\(\Leftrightarrow\)\(\frac{1-\sqrt{1-4x^2}}{x}\)<3\(\Leftrightarrow\)\(\frac{1-\sqrt{\left(1-2x\right)^2}}{x}\)<3\(\Leftrightarrow\)\(\frac{1-\left|1-2x\right|}{x}\)<3\(\Leftrightarrow\)\(\frac{1-\left(1-2x\right)}{x}\)<3\(\Leftrightarrow\)\(\frac{1-1+2x}{x}\)<3\(\Leftrightarrow\)2<3