The inverse functions that correspond to each trigonometric function. As trigonometric functions map many different angles to the same value, a notion of principal value is introduced that determines which of those angle values should be returned. Notation can be problematic, with the following two notations in common use. The first adds the prefix ‘arc’, giving arcsin(x) as the inverse of sin(θ), etc. The second uses the standard inverse function notation, so the inverse of the sine function would be written as sin⁻¹(x).