Question 352342
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Most proofs require that you be able to prove two triangles congruent.

Watch these videos on YouTube:

http://www.youtube.com/watch?v=GgfY66ldfrk

http://www.youtube.com/watch?v=NAhcmPS5k9g&feature=fvw

and some of the others.


Here are some other sites you might try:

Involving SAS, where the corresponding parts are an angle between two sides

http://www.onlinemathlearning.com/triangle-congruence.html

http://www.mathwarehouse.com/geometry/congruent_triangles/side-angle-side-postulate.php

http://www.mathopenref.com/congruentsas.html

http://library.thinkquest.org/20991/geo/ctri.html

http://www.themathpage.com/abooki/propI-4.htm

http://www.jimloy.com/geometry/congruen.htm

http://www.onlinemathlearning.com/congruent-triangles.html

Involving ASA or AAS, where the corresponding parts in two triangles
that you want to prove congruent have two angles and a side corresponding 

http://www.onlinemathlearning.com/triangle-congruency.html

http://www.mathopenref.com/congruentasa.html

http://www.mathwarehouse.com/geometry/congruent_triangles/angle-side-angle-postulate.php

http://www.themathpage.com/abooki/propI-26.htm

Edwin