Tuesday 3 September 2019

How do I show that this series is conditionally convergent?

$$\sum_{n=1}^\infty \cos(n\pi)\sin\left(\frac{\pi}{\sqrt {n}}\right)$$



I know that to show that a series is conditionally convergent, I will have to show that the series is convergent, and also show that the absolute value of the series is divergent.



I am able to show that $$\sum_{n=1}^\infty \cos(n\pi)\sin\left(\frac{\pi}{ \sqrt n}\right)$$ is convergent using the alternating series test, where the limit is equals to 0 and the expression is non-increasing. But I have no idea how to show that the absolute value of the series is divergent. Please correct me if my concept is wrong.

No comments:

Post a Comment

real analysis - How to find $lim_{hrightarrow 0}frac{sin(ha)}{h}$

How to find $\lim_{h\rightarrow 0}\frac{\sin(ha)}{h}$ without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...