`2cos(2x) - 1 = 0` Solve the multiple-angle equation.

Textbook Question

Chapter 5, 5.3 - Problem 39 - Precalculus (3rd Edition, Ron Larson).
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Borys Shumyatskiy | College Teacher | (Level 3) Associate Educator

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`2cos(2x)-1=0,`

`cos(2x)=1/2.`

The general solution is

`2x = +-arccos(1/2)+2kpi,` `kinZZ.`

Because `arccos(1/2) = pi/3,` the final answer is

`x = +-pi/6+kpi,` `kinZZ.`

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