# datatable.math.arccos()¶

Inverse trigonometric cosine of x.

In mathematics, this may be written as $$\arccos x$$ or $$\cos^{-1}x$$.

The returned value is in the interval $$[0, \frac12\tau]$$, and NA for the values of x that lie outside the interval [-1, 1]. This function is the inverse of cos() in the sense that cos(arccos(x)) == x for all x in the interval [-1, 1].