Product and cos

Geometry Level 3

\[\large \displaystyle\prod \limits^{14}_{k=1}\cos \left( \frac{k \pi }{15} \right) =\ ? \]

\[\frac {2}{3}\] \[\frac {1}{2}\] \[\bigg(\frac {1}{2}\bigg)^{14} \] 0 14 \[ -\bigg(\frac {1}{2}\bigg)^{14} \] 1

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