To find the arccosine, or inverse cosine, of a number, we can use the php **acos()** function.

`acos(x)`

In php, we can easily use trigonometric functions from the collection of php math functions. These php math functions allow us to perform trigonometry easily.

To find the arccosine of a number, we use the php **acos()** function.

Below is the php syntax to find the inverse cosine of a number.

`acos(x)`

The input to the **acos()** function must be a float between -1 and 1. The return value will be a float between 0 and pi radians.

```
echo acos(0.5); // 1.0471975511965979
echo acos(0); // 1.5707963267948966
echo acos(-0.75); // 2.4188584057763776
```

## Finding the Inverse Cosine of a Number in php

Arccosine is defined as the inverse of the cosine of a number.

Below, we show that if we pass a number to **cos()** and then call the php **acos()** function, we get back the same number.

```
echo acos(cos(pi()/3)); // 1.0471975511965976
echo pi()/3; // 1.0471975511965976
```

Hopefully this article has been beneficial for you to understand how to use the **acos()** function in php to find the arccosine of a number.

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