Domain of sec^–1x is (–∞,–1]⋃[1,∞)

Domain of tan^–1x is ℝ

Union of (1) and (2) will be domain of given function

(–∞,–1]⋃[1,∞)⋃ℝ

⇒ (–∞,–1]⋃[1,∞)

∴ The domain of given function is (–∞,–1]⋃[1,∞).