function show_div(div_id) {
    // hide all the divs
    document.getElementById('MostPopular').style.display = 'none';
    document.getElementById('Tutorials').style.display = 'none';
    document.getElementById('TipsAndTricks').style.display = 'none';
    document.getElementById('MoreInstructorInfo').style.display = 'none';

    // show the requested div
    document.getElementById(div_id).style.display = 'block';
}

function show_video_div(video_div_id) {
    // hide all the divs
    document.getElementById('AllInfo').style.display = 'none';
    document.getElementById('Notation').style.display = 'none';
    document.getElementById('MP3').style.display = 'none';
    document.getElementById('Jam').style.display = 'none';
    document.getElementById('Images').style.display = 'none';

    // show the requested div
    document.getElementById(video_div_id).style.display = 'block';
}

function show_course_navigation(course_menu_id) {
    //show the course menu on click
    document.getElementByID(course_menu_id).style.display = 'block';
}