\(P=\left(\dfrac{3-\sqrt{x}}{1-x}-\dfrac{\sqrt{x}+3}{x+2\sqrt{x}+1}\right):\dfrac{4}{x^2-2x+1}\\ =\left[\dfrac{\sqrt{x}-3}{x-1}-\dfrac{\sqrt{x}+3}{\left(\sqrt{x}+1\right)^2}\right]:\dfrac{4}{\left(x-1\right)^2}\\ =\left[\dfrac{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}-\dfrac{\left(\sqrt{x}+3\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}\right]:\dfrac{4}{\left(x-1\right)^2}\\ =\dfrac{x-3\sqrt{x}+\sqrt{x}-3-x-3\sqrt{x}+\sqrt{x}+3}{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}\cdot\dfrac{\left(x-1\right)^2}{4}\\ =\dfrac{-4\sqrt{x}}{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)}\cdot\dfrac{\left(\sqrt{x}+1\right)^2\left(\sqrt{x}-1\right)^2}{4}\\ =-\sqrt{x}\left(\sqrt{x}-1\right)\\ =\sqrt{x}-x\)
