The quantities sin−1x, cos−1x, tan−1x are called inverse circular functions. sin−1x is an angle θ, whose sine is x.
The principal value of an inverse function is that value of the general value which is numerically the least. It may be positive or negative. When there are two values, one is positive and the other is negative such that they are numerically equal, then the principal value is the positive one.
Domain and Range