Back to 9.4 Sum-to-Product and Product-to-Sum Formulas

9.4 Exercise 59

Avg difficulty 2.5

Algebraically determine whether each of the given equation is an identity. If it is not an identity, replace the right-hand side with an expression equivalent to the left side. Verify the results by graphing both expressions on a calculator.

$2 \cos \left(2 x\right) \cos x + \sin \left(2 x\right) \sin x = 2 \sin x$

OpenStax Algebra and Trigonometry 2e, 9.4 Sum-to-Product and Product-to-Sum Formulas, exercise 59

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Adapted from College Algebra © 2021 Rice University. Licensed under CC BY 4.0. Sources: College Algebra 2e, Algebra and Trigonometry 2e, Precalculus 2e, College Algebra with Corequisite Support 2e. Imported at revision 4922e46.