${M}$ =$\frac{x}{\sqrt{x}+1}$ +$\frac{\sqrt{x}}{x+\sqrt{x}}$
$a$,$ĐKXĐ:$ $\sqrt{x}$+$1$$\geq$$0$ $⇔$$x$ $\geq$$-1 $
$b$, ${M}$ =$\frac{x}{\sqrt{x}+1}$ +$\frac{\sqrt{x}}{x+\sqrt{x}}$
$=$$\frac{x}{\sqrt{x}+1}$+$\frac{x}{ \sqrt{x}(\sqrt{x}+1) }$
=$\frac{x\sqrt{x}+x}{\sqrt{x}(\sqrt{x} +1) }$
=$\frac{x \sqrt{x} +x}{\sqrt{x}(\sqrt{x} +1) }$
=$\frac{x(\sqrt{x}+1)}{\sqrt{x}(\sqrt{x} +1) }$
=$\frac{x}{\sqrt{x}}$
=$\sqrt{x}$