Arccos(-45)

Real-valued arccos requires its input to be in [-1, 1]. Since -45 is outside, arccos(-45) has no real value.

If you allow complex values, the principal value is: arccos(-45) = π + i arcosh(45) = π + i ln(45 + sqrt(45^2 - 1)) = π + i ln(45 + sqrt(2024)) ≈ 3.141593 + 4.499809 i.