\(x=a-\frac{1}{a}\) với \(a=\sqrt[3]{\sqrt{2}-1}\)
\(\Rightarrow x^3=\left(a-\frac{1}{a}\right)^3=a^3-\frac{1}{a^3}-3\left(a-\frac{1}{a}\right)=a^3-\frac{1}{a^3}-3x\)
\(\Rightarrow x^3+3x=a^3-\frac{1}{a^3}=\sqrt{2}-1-\frac{1}{\sqrt{2}-1}=\sqrt{2}-1-\left(\sqrt{2}+1\right)=-2\)
\(\Rightarrow P=x^3+3x+2008=-2+2008=2006\)