Maths Triangle Angles

Today in Maths we learnt about triangles. More specifically, we learnt about the third angle of a triangle and about the reverse angles of a triangle. What I mean by this is...

Third Angle:

1st interior angle + 2nd interior angle = x

180 - x = 3rd interior angle

Reverse Angle:

1st interior angle + 2nd interior angle = 1st exterior angle

Does anyone know any other formulas involving the angles or sides of a triangle?