In order for you to understand the different types of triangles you must know this theorem

Theorem: The sum of the measures of the three angles of a triangle is 180 degrees.  Here is a proof of this theorem. Given:  Triangle ABC Prove:  Angle A plus Angle B             Plus Angle C equals            to 180 degrees. According to the Parallel Postulate, there exists only one line through point A parallel to line BC. Because of the straight angle, we know that angle 1 plus angle 2 plus angle 3 euqals to 180 degrees.  Since angle 1 is congruent to angle B and angle 3 is congruent to angle C because of (If parallel lines then alternate interior angles are congruent.  We can substitue to obtain angle B plus angle 2 plus angle C is equal to 180 degrees. so angle A plus angle B plus angle C is equal to 180 degrees.

A

B                                      C

Enter Types of Triangles

"Theorems are hard at first, but they get easier when you get into congruent triangles."