2.12.4 Asymptotic analysis

Problem: Write down the asymptotic formula for the function: \[ \begin{array}{l} f(x)=\sqrt{x^{4}+2 x^{2}-2 x}-x^{2} \cos \frac{x}{x^{2}+1}, \\ x \rightarrow+\infty . \end{array} \]