$\displaystyle \begin{array}{{>{\displaystyle}l}} B1:\ ĐKXD\ x\geqslant 0;\ x\neq 4\\ P=\frac{x+12+\sqrt{x} -2-4\sqrt{x} -8}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)} =\frac{x-3\sqrt{x} +2}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)}\\ =\frac{\left(\sqrt{x} -2\right)\left(\sqrt{x} -1\right)}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)} =\frac{\sqrt{x} -1}{\sqrt{x} +2}\\ B2:\ DKXĐ:x >0\\ P=\frac{x-2-\sqrt{x} -2+\sqrt{x}}{\sqrt{x}\left(\sqrt{x} +2\right)} =\frac{x-4}{\sqrt{x}\left(\sqrt{x} +2\right)}\\ =\frac{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)}{\sqrt{x}\left(\sqrt{x} +2\right)} =\frac{\sqrt{x} -2}{\sqrt{x}}\\ B3:\ ĐKXĐ:\ x\geqslant 0;\ x\neq 1\\ P=\frac{x+\sqrt{x} -2\sqrt{x} +2-2}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)} =\frac{x-\sqrt{x}}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)}\\ =\frac{\sqrt{x}\left(\sqrt{x} -1\right)}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)} =\frac{\sqrt{x}}{\sqrt{x} +1}\\ B4:\ ĐKXĐ:\ x\geqslant 0;\ x\neq 4\\ P=\frac{x+\sqrt{x} +2+\sqrt{x} -2}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)} =\frac{x+2\sqrt{x}}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)}\\ =\frac{\left(\sqrt{x} +2\right)(\sqrt{x}}{\left(\sqrt{x} +2\right)\left(\sqrt{x} -2\right)} =\frac{\sqrt{x}}{\sqrt{x} -2}\\ B5:\ \ ĐKXĐ:\ x\geqslant 0;\ x\neq 1\\ P=\frac{x+\sqrt{x} -3\sqrt{x} +3-6\sqrt{x} +4}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)} =\frac{x-8\sqrt{x} +7}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)}\\ =\frac{\left(\sqrt{x} -7\right)\left(\sqrt{x} -1\right)}{\left(\sqrt{x} +1\right)\left(\sqrt{x} -1\right)} =\frac{\sqrt{x} -7}{\sqrt{x} +1} \end{array}$