The **`is_nan()` function** in PHP returns `true` (`1`) if the value is NaN; otherwise, it returns `false`. Some of the operations that can return a NaN include: division by zero, calculating the square root of a negative number, trying to pass an invalid value to an inverse trigonometric function, and the arc cosine of a value that does not lie in the range negative one to one.

Figure 1 shows the visual representation of the `is_nan()` function.

#      
#  Syntax
```php
bool is_nan(number)
```
#     
#  Parameter
This function requires the number as a parameter.

##     
## Return value
This function returns `true` (`1`) if the value is NaN; otherwise, it returns `false`. 

##    
## Example
The following example shows how to use `is_nan()` in PHP.

<?php
#number 
echo("is_nan(10): ");
echo (is_nan(10));
echo("\n");
echo("is_nan(-5.3): ");
echo (is_nan(5.3));
echo("\n");
?>	

<?php
#nan
echo("is_nan(0/0): ");
echo (is_nan(0/0));
echo("\n");
echo("is_nan(acos(2)): ");
echo (is_nan(acos(2)));
?>


What is is_nan() in PHP?

Returns true if the value is NaN; otherwise, it returns false. Used in specific math errors.