# Chapter 13 - The Trigonometric Functions - Chapter Review - Review Exercises - Page 701: 4

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#### Work Step by Step

We have the following identities $\cos(x+y)=\cos x \cos y -\sin x \sin y$ so the right answer for $cos(a+b)$ must be $\cos(a+b)=\cos a \cos b - \sin a \sin b$

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