When do we use Trigonometric identities, ratios, and laws. And why do we need cosine & sine ...

Trigonometric identities are used to rewrite trigonometric expressions to manipulate the form of the expression, often to be able to solve equations. The basic trigonometric identities can be logically deduced from the definitions and graphs of the six trigonometric functions.


These laws are used to help us find unknown angles in triangles. For example, if we're given a triangle with unknown lengths or sides, depending on the configuration of the sides and angles, these formulas can be employed to find the remaining unknowns in the question.