\(a,x=25\Leftrightarrow A=\dfrac{3\cdot5-4}{5-1}=\dfrac{11}{4}\\ b,B=\dfrac{x+\sqrt{x}+3\sqrt{x}-3-6\sqrt{x}+4}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\\ B=\dfrac{x-2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\dfrac{\left(\sqrt{x}-1\right)^2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\dfrac{\sqrt{x}-1}{\sqrt{x}+1}\\ c,B=\dfrac{1}{4}\Leftrightarrow4\sqrt{x}-4=\sqrt{x}+1\Leftrightarrow3\sqrt{x}=5\\ \Leftrightarrow x=\dfrac{25}{9}\left(tm\right)\\ d,P=AB=\dfrac{3\sqrt{x}-4}{\sqrt{x}-1}\cdot\dfrac{\sqrt{x}-1}{\sqrt{x}+1}=\dfrac{3\sqrt{x}-4}{\sqrt{x}+1}\\ P=\dfrac{3\left(\sqrt{x}+1\right)-7}{\sqrt{x}+1}=3-\dfrac{7}{\sqrt{x}+1}\\ P< 3\left(\dfrac{7}{\sqrt{x}+1}>0\right)\)
