\(3,\\ a,A=\dfrac{3-5}{3}=-\dfrac{2}{3}\\ b,P=AB=\dfrac{\sqrt{x}-5}{\sqrt{x}}\cdot\dfrac{x+5\sqrt{x}-3\sqrt{x}}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\\ P=\dfrac{\sqrt{x}\left(\sqrt{x}+2\right)}{\sqrt{x}\left(\sqrt{x}+5\right)}=\dfrac{\sqrt{x}+2}{\sqrt{x}+5}\)
\(2,\\ a,ĐK:x\ge0\\ PT\Leftrightarrow6\sqrt{x}+15\sqrt{x}-12\sqrt{x}=18\\ \Leftrightarrow\sqrt{x}=2\Leftrightarrow x=4\left(tm\right)\\ b,ĐK:x\ge-2\\ PT\Leftrightarrow\left|2x-1\right|=x+2\\ \Leftrightarrow\left[{}\begin{matrix}2x-1=x+2\left(x\ge-2\right)\\1-2x=x+2\left(x< -2\right)\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\left(tm\right)\\x=-\dfrac{1}{3}\left(ktm\right)\end{matrix}\right.\\ \Leftrightarrow x=3\)
\(1,\\ a,=7\cdot12+3+4\sqrt{7}=87+4\sqrt{7}\\ b,=\dfrac{\sqrt{5}\left(\sqrt{3}-5\right)}{\sqrt{3}-5}+\sqrt{5}-1-\dfrac{\sqrt{5}-2}{5-4}\\ =\sqrt{5}+\sqrt{5}-1-\sqrt{5}+2=\sqrt{5}+1\)
