Cambridge O Level Additional Mathematics · Syllabus 4037 · Trigonometry
Trigonometric Proof
What is Trigonometric Proof?
A trigonometric proof establishes that two expressions are equal for every angle at which both are defined. It is carried out by choosing one side, usually the more complicated one, and transforming it through valid algebra and the supplied identities until it becomes the other side. The result being proved must never be used as a starting point, and no step may divide or cancel by an expression that could be zero unless that expression is known to be non-zero on the domain. The proof concludes by stating the common domain, that is the set of angles at which both original sides are defined.
This definition is part of the Trigonometry chapter in Cambridge O Level Additional Mathematics.