Recall that the interior (inside) angles of a triangle add up 180[math]^\circ[/math]. 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[math]^\circ[/math].

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 [math]\angle[/math]BAC) to verify. For the second animation, drag the slider to visually observe the relationship.