The range of $f(x) = 4 \sin^{-1}\left(\frac{x^2}{x^2 + 1}\right)$ is:
Step-by-Step Solution
Key Concept: Note that $x^2/(x^2 + 1) \in [0, 1)$ for all real $x$. Apply the range of $\sin^{-1}$ on $[0, 1)$, then multiply by 4.
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Correct Answer: (2)