The **`sqrt()` function** in PHP returns the square root of a non-negative number. 

Figure 1 below shows the mathematical representation of the `sqrt()` function.

#   
#  Syntax
```php
float sqrt(number)
```

#   
#  Parameter

`sqrt()` requires a non-negative number as a parameter. If the number is negative, then this function returns `NaN`.

##  
## Return value

`sqrt()` returns the square root of the number sent as a parameter.

##  
## Code

The following example shows how to use the `sqrt()` function in PHP.

<?php
echo("sqrt(4): ");
echo (sqrt(4));
echo("\n");
echo("sqrt(0): ");
echo (sqrt(0));
echo("\n");
echo("sqrt(25): ");
echo (sqrt(25));
echo("\n");
echo("sqrt(4.5): ");
echo (sqrt(4.5));
echo("\n");
#error output
echo("sqrt(-4): ");
echo (sqrt(-4));
?>

What is sqrt() in PHP?

PHP's sqrt() function returns the square root of a non-negative number, returning NaN for negatives.