What steps should be taken to ensure that the necessary extension is properly included in the php.ini file for defining functions in PHP?

To ensure that the necessary extension is properly included in the php.ini file for defining functions in PHP, you should locate the extension directive in the php.ini file and uncomment it by removing the semicolon at the beginning of the line. Make sure to specify the correct path to the extension file. Save the php.ini file and restart the web server for the changes to take effect.

;extension=your_extension.so
``` 

Change the above line to:

```php
extension=your_extension.so