# NumPy arccos()

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The NumPy `arccos()` function is the trigonometric inverse cosine function so that, if y = cos(x), then x = arccos(y). If you apply it to a NumPy array, it performs the function element-wise.

`numpy.arccos(x, out=None, where=True, <optional keyword arguments>)`

The following table shows the return value of the function:

Related: `cos`, `arctan`, `arcsin`, `emath.arccos`

## Notes

`arccos` is a multivalued function: for each x there are infinitely many numbers z such that cos(z) = x. The convention is to return the angle z whose real part lies in [0, pi].

For real-valued input data types, `arccos` always returns real output. For each value that cannot be expressed as a real number or infinity, it yields `nan` and sets the invalid floating point error flag.

For complex-valued input, `arccos` is a complex analytic function that has branch cuts [-inf, -1] and [1, inf] and is continuous from above on the former and from below on the latter.

The inverse `cos` is also known as acos or cos^-1.

Let’s dive into some examples to show how the function is used in practice:

### Examples

Any master coder has a “hands-on” mentality with a bias towards action. Try it yourself—play with the function in the following interactive code shell:

Exercise: Modify the linspace() function so that you plot the arccos from -100 to +100!

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