If $\theta=\pi / 7$, then $\cos \theta+\cos 3 \theta+\cos 5 \theta$ is

JEE MATHEMATICS MCQ: MULTIPLE AND SUBMULTIPLE ANGLES

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Analyzing +4 | -1

\theta=\pi / 7

, then

\cos \theta+\cos 3 \theta+\cos 5 \theta

View answer and explanation

Correct option: A

\frac{1}{2}

Option A (

\frac{1}{2}

) is correct because the sum of the cosines can be simplified to

\frac{1}{2}

when

\theta = \frac{\pi}{7}

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