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What is the general term $(a_n)$ of the alternating sequence $\displaystyle \cos \left( \frac{3n \pi}{2} \right)$ from $1$ to $\infty$, $n \in \mathbb{N}$ ?

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    Does t = n? Have you tried evaluating a few terms yourself?2011-01-04
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    This is alternating, and furthermore it is periodic with 4t. This should be enough for solving that...2011-01-04
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    $cos(3t \pi/2): cos(3 \pi/2)=0, cos(3\pi)=-1, cos(9 \pi/2)=0, cos(6 \pi) = 1 \cdots$, but general rule is missing in my mind.2011-01-04

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