- #1
s3a
- 818
- 8
Homework Statement
For the series Σ_{n=1} ^{∞} {(4 – cos(n^2))/n^2} (this series can also be seen by looking at TheSeries.png.),
which of the following is true?:
A. This series converges.
B. This series diverges.
C. The integral test can be used to determine convergence of this series.
D. The comparison test can be used to determine convergence of this series.
E. The limit comparison test can be used to determine convergence of this series.
F. The ratio test can be used to determine convergence of this series.
G. The alternating series test can be used to determine convergence of this series.
Homework Equations
N/A
The Attempt at a Solution
I think only A and D being true is the answer, but why isn't that the case?
I think that A is true, because the numerator of that series ranges from 3 to 5 both, and all the numbers in that interval are smaller than 1 and 1/n^2 is a convergent p-series.
I think that B is false, because A is true.
I think that C is false, because it involves a Fresnel integral which is material that is more advanced than that of this course, but Wolfram Alpha says that this does converge, so I'm not sure what to assume here. I'd appreciate some elaboration on this one.
I think that D is true, and it is the reason I used to justify A.
I think that E is false, because the value of the numerator ranges from 3 to 5, and since there is no one value, the limit doesn't exist.
I think that F is false, because the cosine functions make the limit unpredictable, therefore it does not exist.
I think that G is false, because the alternating series applies to functions where there is a predictable negative or positive sign, instead of a range of values which occasionally reach -1 or 1 (and other values in between).
Could someone please tell me why I'm wrong?