ĐKXĐ: \(-1< x< 1\)
\(A=\frac{5-3x}{\sqrt{\left(1+x\right)\left(1-x\right)}}=\frac{4\left(5-3x\right)}{2\sqrt{\left(1+x\right)\left(4-4x\right)}}\ge\frac{4\left(5-3x\right)}{\left(1+x\right)+\left(4-4x\right)}=\frac{4\left(5-3x\right)}{5-3x}=4\)
\(\Rightarrow A_{min}=4\) khi \(1+x=4-4x\Leftrightarrow x=\frac{3}{5}\)