Giải thích các bước giải:

a.Ta có:

$P=\dfrac{x^2-\sqrt{x}}{x+\sqrt{x}+1}-\dfrac{2x+\sqrt{x}}{\sqrt{x}}+\dfrac{2(x-1)}{\sqrt{x}-1}$

$\to P=\dfrac{\sqrt{x}(\sqrt{x}-1)(x+\sqrt{x}+1)}{x+\sqrt{x}+1}-\dfrac{\sqrt{x}(2\sqrt{x}+1)}{\sqrt{x}}+\dfrac{2(\sqrt{x}-1)(\sqrt{x}+1)}{\sqrt{x}-1}$

$\to P=\sqrt{x}(\sqrt{x}-1)-(2\sqrt{x}+1)+2(\sqrt{x}+1)$ 

$\to P=x-\sqrt{x}+1$

b.Để $P=7$

$\to x-\sqrt{x}+1=7$

$\to x-\sqrt{x}-6=0$

$\to (\sqrt{x}-3)(\sqrt{x}+2)=0$

$\to \sqrt{x}=3$ vì $\sqrt{x}+2>0$

$\to x=9$