**Definition:**We can use the Atan () function to figure out the arc tangent of a number. We can also use the Atan2 () function to figure out the arc tangent of a point given two coordinates. It is written as

*atan(Y,X)*and calculates the arc tangent of Y/X. The result will always be between -PI and PI radians.

**Also Known As:**Arc Tangent, Arctangent

**Examples:**

```
<?php
echo(atan2(5,5) . "<br />");
echo(atan2(-3,4))
?>
```

This will return:

0.78539816339745

-0.64350110879328

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