$\require{cancel}$Investigate for convergence or divergence:
$$\sum_{i=1}^\infty \frac{3^n+4^n}{4^n+5^n}$$
I'm allowed to use basic tests for convergence or divergence:
- P-series test
- Geometric series test
- nth Term test
- Integral test
- Comparison test
- Limit Comparison test
- Ratio test
- Root test
- Alternating test
The bold items are the ones I think are more likely to be used in this problem as opposed to the others.
Progress
So I made some progress but I'm not sure how to proceed.
I assume,$$a_n=\frac{3^n+4^n}{4^n+5^n}$$and,$$b_n=\frac{\cancel{3^n}+4^n}{\cancel{4^n}+5^n}=\frac{4^n}{5^n}=\left(\frac{4}{5}\right)^n$$The reason I cancelled the $3^n$ and the $4^n$ is because they're insignificant when compared to $4^n$ and $5^n$, respectively.
At this point, I know that $\sum_{i=1}^\infty b_n$ converges, because it is a geometric series. But I'm not sure how to proceed from here.