arctan range and domain: ℝ → (−π/2, π/2)
arctan accepts every real number and returns an angle in (−π/2, π/2). The interval is open, not closed: tangent has asymptotes at ±π/2, so those endpoints are approached but never reached.
Related Inverse identities
Practise it
Reading a formula is not the same as recalling it under time pressure. The workspace drills Inverse questions in the quiz, and the triangle solver shows a worked solution for any triangle you type in.
Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.