$\mathop \sum \limits_{r = 1}^{n - 1} \,\,{\cos ^2}\,\,\frac{{r\;\pi }}{n}$ is equal to

JEE MATHEMATICS MCQ: MULTIPLE AND SUBMULTIPLE ANGLES

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Application +4 | -1

\sum \limits_{r = 1}^{n - 1} \,\,{\cos ^2}\,\,\frac{{r\;\pi }}{n}

is equal to

View answer and explanation

Correct option: C

\frac{n}{2} - 1

Option C (

\frac{n}{2} - 1

) is correct because the summation of the cosine squared terms simplifies to this expression using trigonometric identities and series summation.

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