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Trigonometry

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Multiple Angles: Cosines without Using Double Angle Formulas

TRIG-YNEEEH

Find the exact solutions in the interval $[0,2\pi )$ for the following equation:

$$2\cos { 2\theta } -\sqrt { 2 } =0$$

A

$\theta =\cfrac { \pi }{ 8 } ,\cfrac { 7\pi }{ 8 }$

B

$\theta =\cfrac { \pi }{ 4 } ,\cfrac { 7\pi }{ 4 } $

C

$\theta =\cfrac { \pi }{ 4 } ,\cfrac { 3\pi }{ 4 } $

D

$\theta =\cfrac { \pi }{ 8 } ,\cfrac { 3\pi }{ 8 } $