$$\sum\limits_{n=2}^\infty \frac{\cos(n\pi)}{\ln(n)^2}$$
I'm not sure how this would conditionally converge, according to my calculations I would assume it's absolutely converge.
2026-03-25 05:07:00.1774415220
Could I get an explanation on why this would conditionally converge?
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Note that $\cos(n\pi) = (-1)^n$.
This converges by the alternating series test. Compare to the harmonic series to see that it does not converge absolutely.