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How do you evaluate $[cos (\frac{π}{5}) \cdot cos (2 \frac{π}{5})]$ $[cos(pi/5) * Cos(2pi/5)]$ ?

1 Answer

Apr 18, 2016

This product is equal to 1/4.

Explanation:

See here for a proof:

https://socratic.org/questions/how-do-you-prove-cos36-cos72-1-4#250226

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