While the letter F is reflected here, the lesson being shown applies to all reflections. check each box separately/together to learn how the coordinates relate the mirron (the y-axis here for ease of learning.

[url=http://www.maa.org/sites/default/files/images/upload_library/47/Crowe/GeoGebra_Activity_1.html[/url] by Cheryll E. Crowe, Eastern Kentucky University