The main tr.nometric iden.ies between tr.nometric functions are proved, using mainly the geometry of the right triangle. For greater and negative angles, .Proving Tr.nometric Iden.ies. Proving an iden.y is very different in concept from solving an equation. For instance, sin x = 1/csc x is an iden.y. To "prove" an iden.y, you have to use logical steps to show that one side of the equation can be transformed into the other side of the equation..