Study GuideTrigonometry–Trigonometric Identities1. Addition IdentitiesIn the previous section, we worked with basic identities that involved onlyone variable.Now we’re going a step further.In this section, we introduce identities that involvetwo angles. These are calledtrigonometricaddition identities.Here they are:These four formulas are sometimes called:•Sum identity for sine•Difference identity for sine•Sum identity for cosine•Difference identity for cosineThey may look a little heavy at first, but don’t worry—once you see them in action, they start to feelvery natural.These identities can be proven using basic trigonometric facts and the distance formula in thecoordinate plane. In this section, we’ll focus mainly on understanding how to use them.Example1:Rewriteas a trigonometric function involving only one angle.Preview Mode
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