a: \(P=2\cdot\dfrac{\sqrt{x}-\sqrt{x}+1}{\sqrt{x}\left(\sqrt{x}-1\right)}\cdot\dfrac{x\left(x-1\right)}{\sqrt{x}+1}\)
\(=2\cdot\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)}{\sqrt{x}+1}=2\sqrt{x}\)
b: Để P=can 2018 thì căn x=căn 2018/2
hay \(x=\left(\dfrac{\sqrt{2018}}{2}\right)^2=\dfrac{2018}{4}=504.5\)