Identities expressing trig functions in terms of their complements. This is probably the most important trig identity.
The Pythagorean formula for sines and cosines. But these you should.ĭefining relations for tangent, cotangent, secant, and cosecant in terms of sine and cosine.
You don’t have to know all the identities off the top of your head. These identities mostly refer to one angle denoted θ, but there are some that involve two angles, and for those, the two angles are denoted α and β. It is convenient to have a summary of them for reference.
You have seen quite a few trigonometric identities in the past few pages.
