a) $P=(\frac{1}{\sqrt{x}-1}+\frac{1}{\sqrt{x}+1}):\frac{\sqrt{x}}{\sqrt{x}-1}\\=[\frac{\sqrt{x}+1+\sqrt{x}-1}{(\sqrt{x}-1)(\sqrt{x}+1)}].(\frac{\sqrt{x}-1}{\sqrt{x}})\\=(\frac{2\sqrt{x}}{\sqrt{x}+1}).\frac{1}{\sqrt{x}}\\=\frac{2}{\sqrt{x}+1}$
b)$P=\frac{1}{3}\\\Rightarrow...