Giúp mình với

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
a,\ P=\frac{x-\sqrt{x}}{x-1} +\frac{2\sqrt{x}}{\sqrt{x} +1} -1\ ( x\geqslant 0;x\neq 1)\\
P=\frac{\sqrt{x} .\left(\sqrt{x} -1\right)}{\left(\sqrt{x} -1\right)\left(\sqrt{x} +1\right)} +\frac{2\sqrt{x}}{\sqrt{x} +1} -1\\
P=\frac{\sqrt{x}}{\sqrt{x} +1} +\frac{2\sqrt{x}}{\sqrt{x} +1} -\frac{\sqrt{x} +1}{\sqrt{x} +1}\\
P=\frac{2\sqrt{x} -1}{\sqrt{x} +1}
\end{array}$ 
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
b,\ P=\frac{-1}{2}\\
\Leftrightarrow \frac{2\sqrt{x} -1}{\sqrt{x} +1} =-\frac{1}{2}\\
\Leftrightarrow 4\sqrt{x} -2=-\sqrt{x} -1\\
\Leftrightarrow 5\sqrt{x} =1\\
\Leftrightarrow \sqrt{x} =\frac{1}{5}
\end{array}$
$\displaystyle \Leftrightarrow x=\frac{1}{25}$ (thỏa mãn điều kiện xác định)
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
c,\ x^{2} =28-16\sqrt{3} =4^{2} -2.4.2\sqrt{3} +\left( 2\sqrt{3}\right)^{2} =\left( 4-2\sqrt{3}\right)^{2}\\
\Leftrightarrow x=4-2\sqrt{3} =\left(\sqrt{3} -1\right)^{2}\\
\Rightarrow \sqrt{x} =\sqrt{3} -1
\end{array}$
Khi đó $\displaystyle P=\frac{2.\left(\sqrt{3} -1\right) -1}{\sqrt{3} -1+1} =\frac{2\sqrt{3} -3}{\sqrt{3}} =2-\sqrt{3}$
$\displaystyle d,\ P=\frac{2\sqrt{x} -1}{\sqrt{x} +1} =\frac{2\sqrt{x} +2}{\sqrt{x} +1} -\frac{3}{\sqrt{x} +1} =2-\frac{3}{\sqrt{x} +1}$
P nguyên khi và chỉ khi 
$\displaystyle \frac{3}{\sqrt{x} +1} \in Z$
$\displaystyle \Leftrightarrow \sqrt{x} +1\in \{1;3\}$ (vì $\displaystyle \sqrt{x} +1 >0\forall x)$
$\displaystyle  \begin{array}{{>{\displaystyle}l}}
\Leftrightarrow \sqrt{x} \in \{0;2\}\\
\Leftrightarrow x\in \{0;4\}
\end{array}$
2 giá trị trên đều thỏa mãn