Series 215 problem 04.html

Given the series . We may argue that this series is convergent by using the comparison tests. First, we note the series under consideration is a positive term series, and for all . Recall converges since it is a p-series with . Therefore by the Comparison Test, the series is convergent. Alternatively we could argue from the Limit Comparison Test: Notice that , and therefore the series is convergent. Now, since we know that the series converges, we will use Maple to sum the first 10 terms of this series, this is easy:

> sum(1/(n^4+n^2),n=1..10);

Perhaps an approximation is ok in this case.

> evalf(sum(1/(n^4+n^2),n=1..10));

Now, how close is this number to the actual sum. The error in this case is underneath .

> evalf(sum(1/(n^4+n^2),n=1..infinity));

And we see that our above estimate above is within .003 of the actual sum.

Submission:

Use the sum of the first 10 terms to approximate the sum of the given series. Use the Integral test remainder estimate to get an upper bound on the error. Be careful to justify that the series converges before approximating the sum.

(a)

(b)

Submission worksheet:

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2. Alternating series test.

The series is an alternating series. We want to determine the value of p so that this series is convergent. The alternating series test is helpful here. First notice that for all n where as long as . This means the sequence of the absolute values of the terms of the series is decreasing as long as . Secondly, if . Therefore, the conditions of the Alternating Series Test are met as long as , thus the series is convergent. Now let us be more specific and choose and estimate the sum in this case with an error no bigger than 0.01. By the Alternating Series Estimation Theorem, we know that this surely happens if . This is a fairly easy inequality to solve, and we get . So, summing the first 9 terms of the series will give an error no greater than 0.01.