Đáp án:
$\displaystyle B=\sqrt{x+3} +\sqrt{x-3} -3$
Giải thích các bước giải:
$\displaystyle \begin{array}{{>{\displaystyle}l}} B=\sqrt{( x-3) -2\sqrt{x-3} +1} -\sqrt{x-3-2.2\sqrt{x-3} +4}\\ B=\sqrt{\left(\sqrt{x+3} -1\right)^{2}} -\sqrt{\left(\sqrt{x-3} -2\right)^{2}}\\ B=|\sqrt{x+3} -1|-|\sqrt{x-3} -2|\\ Với\ 3\leqslant x\leqslant 4\Rightarrow \sqrt{x+3} >1;\ \sqrt{x-3} < 2\\ \Rightarrow B=\sqrt{x+3} -1-\left( 2-\sqrt{x-3}\right)\\ B=\sqrt{x+3} +\sqrt{x-3} -3 \end{array}$
