1. This is an introduction to the major topics in trigonometry. As always, don't forget to do the problems at the end of the lessons.And...don't forget to leave acomment on the page letting us knowwhether the link was helpful to you.

 Here is a very simple explanations showing how the law of cosine works. It includes an interactive demo to help you visualize the concepts.

 Here is a 'proof of concept' for the law of cosine.

 Here is a demonstration of the congruence using triangles.

 An explanation and demo of angles and parallel lines.

 Try a parallel line problem now.

 Try another angle and parallel line problem. You can use the interactive demo to help you.