How to inlucde external javascipt libraries

[eluser]Unknown[/eluser]
I have a web page which needs to include external javascript libraries. I have downloaded them and include in the php->libraries folder. My application is hosted in openshift cloud. I want to include those javascript files in my php file. I have used this code

script src="../../libraries/dhtmlxCalendar/dhtmlxCalendar/codebase/dhtmlxcalendar.js">

But it is not working

then I tried

script type="text/javascript" src="<?php echo base_url();?>js/jquery.js" >

The base url gives me the url but it is also not working.

What is the correct way for this ? I am a beginner for codeigniter. Could you help me