# acos()

The inverse of [](sketch_cos), returns the arc cosine of a value.

## Examples

<div class="example-table">

<div class="example-row"><div class="example-cell-image">

</div><div class="example-cell-code">

```python
def setup():
    a = py5.PI
    c = py5.cos(a)
    a_c = py5.acos(c)
    # prints "3.1415927 : -1.0 : 3.14159261"
    py5.println(round(a, 8), ':', round(c, 8), ':', round(a_c, 8))
```

</div></div>

<div class="example-row"><div class="example-cell-image">

</div><div class="example-cell-code">

```python
def setup():
    a = py5.PI + py5.PI/4
    c = py5.cos(a)
    a_c = py5.acos(c)
    # prints "3.92699087 : -0.70710674 : 2.35619443"
    py5.println(round(a, 8), ':', round(c, 8), ':', round(a_c, 8))
```

</div></div>

</div>

## Description

The inverse of [](sketch_cos), returns the arc cosine of a value. This function expects the values in the range of -1 to 1 and values are returned in the range `0` to `PI`.

This function makes a call to the numpy `acos()` function.

## Signatures

```python
acos(
    value: Union[float, npt.ArrayLike],  # value in the range of -1 to 1 whose arc cosine is to be returned
) -> Union[float, npt.NDArray]
```

Updated on August 23, 2025 19:59:53pm UTC