# .arccos()

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Published Aug 26, 2024
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In NumPy, the `.arccos()` function calculates the inverse cosine (arccosine), of each element in an array. The elements in the array should be cosine values, which must lie within the range [-1, 1]. The function returns the corresponding angle in radians for each cosine value.

## Syntax

``````numpy.arccos(array, out = None, where=True)
``````
• `array`: An array-like or scalar containing cosine values. The function computes the inverse cosine of each element.
• `out`: An optional parameter specifying an array where the result will be stored. If not provided, a new array is created.
• `where`: A condition or boolean array that determines which elements of `array` are used to compute the inverse cosine. The inverse cosine is computed only for elements where the condition is `True`; other elements remain unchanged.

## Example

In the example below, the `.arccos()` function calculates the inverse cosine of each element in a NumPy array and prints the resulting angles in radians:

```import numpy as np
# Array of cosine values within the range [-1, 1]cos_values = np.array([1, 0, -1])
# Compute the arccosine of each elementangles_in_radians = np.arccos(cos_values)
```

The output would be:

```Arccosine:  [0.         1.57079633 3.14159265]
```

Note: The function returns `NaN` for values outside the range [-1, 1], since the arccosine is not defined for those values.

## Codebyte Example

Run the following code to understand how the `.arccos()` function works:

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