\(đk:-1< x< 1\Rightarrow P=\left(\dfrac{2}{\sqrt{1+x}}+\dfrac{\sqrt{1-x^2}}{\sqrt{1+x}}\right):\left(\dfrac{2+\sqrt{1-x^2}}{\sqrt{1-x^2}}\right)=\left(\dfrac{2+\sqrt{1-x^2}}{\sqrt{1+x}}\right):\left(\dfrac{2+\sqrt{1-x^2}}{\sqrt{1-x^2}}\right)=\dfrac{\sqrt{1-x^2}}{\sqrt{1+x}}=\sqrt{1-x}\)
\(P< 1\Leftrightarrow\sqrt{1-x}< 1\Leftrightarrow1-x< 1\Leftrightarrow x>0\Rightarrow0< x< 1\)