$\sum\frac{(-1)^{n+1}}{2n^2-3n\cos(n\pi)}$ show that this is convergence or divergence.
Ok i couldnt find a way to show this using the alternating series test. And when i used the ratio test i found that it was equal or smaller than one meaning i cant draw a conclusion. ratio test:
lim$\frac{2n^2-3n\cos(n\pi)}{2(n+1)^2-3(n+1)\cos(n\pi)}$ this is equal or smaller than lim$\frac{2n^2+3n}{2n^2-3n}=1$ so it is smaller or equal than 1 so it doesnt help me.
What should i do somebody can help me?