Solve: $\tan^{-1}(x + 1) + \tan^{-1}(x - 1) = \tan^{-1}\left(\frac{8}{31}\right)$
Step-by-Step Solution
Key Concept: Apply the $\tan^{-1}$ addition formula to the left side, cross-multiply, and factor the resulting quadratic. Reject roots that violate the domain.
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Correct Answer: (1)