Trigonometric Identities
Subject:
Trigonometry [1]
Tags:
Trig Identites [3]
AN IDENTITY IS AN EQUALITY that is true for any value of the variable. (An equation is an equality that is true only for certain values of the variable.)
In algebra, for example, we have this identity:
(x + 5)(x − 5) = x² − 25.
The significance of an identity is that, in calculation, we may replace either member of the identity with the other. We use an identity to give an expression a more convenient form. In calculus and all its applications, the trigonometric identities are of central importance.
On this page, we will present the main identities. The student will have no better way of practicing algebra than by proving them. Links to the proofs appear below.
Reciprocal identities
sin θ = 1
csc θ csc θ = 1
sin θ