∞∑n=1sin2(πn)
First, I tried Divergence test, but the limit is 0, so that's inconclusive. I don't think I can do integral test, since it's not a clean integration.
Did I do this right ? If it's wrong, can you steer me in the right direction? I tried subbing in 1−cos(x) for the sin(x). This would get:
∞∑n=1sin2(πn)
=∞∑n=11−cos2(πn)
=∞∑n=11−∞∑n=1sin2(πn)
But that first sigma is divergent to infinity, so does the original series also diverge to infinity?
The tests I know are: Geometric, p-series, Divergence (nth term) test, Integral test, Direct Comparison test, Alternating Series Test, Absolute convergence, and Ratio test.
Answer
Using sin(x)≤x for all x≥0 so by comparison with the convergent series ∑1n2 we conclude the convergence of the given series.
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