Use the interactive animation below to manipulate vertex "C". Try to form the 6 triangle types from above.

Recall that the interior (inside) angles of a triangle add up 180. Manipulate the triangle below to verify.

There are two exterior (outside) angle relationships to consider for triangles. For the first relationship, the exterior angles of a triangle all add up to 360.

In the second relationship, an exterior angle equals the sum of the two opposite interior angles. Use the animation below to illustrate. In the animation below, drag Point A (or BAC) to verify. For the second animation, drag the slider to visually observe the relationship.