Giải thích các bước giải:
a.Ta có :
$P=\dfrac{x\sqrt{x}-8}{x+2\sqrt{x}+4}+3(1-\sqrt{x})$
$\to P=\dfrac{(\sqrt{x})^3-2^3}{x+2\sqrt{x}+4}+3(1-\sqrt{x})$
$\to P=\dfrac{(\sqrt{x}-2)(x+2\sqrt{x}+4)}{x+2\sqrt{x}+4}+3(1-\sqrt{x})$
$\to P=\sqrt{x}-2+3(1-\sqrt{x})$
$\to P=1-2\sqrt{x}$
b.$Q=\dfrac{2(1-2\sqrt{x})}{1-(1-2\sqrt{x})}$
$\to Q=-2+\dfrac{2}{\sqrt{x}}$
$\to Q\in Z\to \dfrac{2}{\sqrt{x}}\in Z$
$\to \sqrt{x}\in\{1,2\}$
$\to x\in\{1,4\}$
