{"id":10712,"date":"2017-08-31t10:02:58","date_gmt":"2017-08-31t17:02:58","guid":{"rendered":"\/\/www.catharsisit.com\/hs\/?p=10712"},"modified":"2018-10-24t03:57:20","modified_gmt":"2018-10-24t10:57:20","slug":"ap-calculus-bc-review-alternating-series","status":"publish","type":"post","link":"\/\/www.catharsisit.com\/hs\/ap\/ap-calculus-bc-review-alternating-series\/","title":{"rendered":"ap calculus bc review: alternating series"},"content":{"rendered":"
an alternating series is one in which the signs of the terms switch between positive and negative. these kinds of series show up fairly regularly in applications. so it’s important to know how to work with them.<\/p>\n
in this review article, we’ll examine the properties of alternating series. we’ll also work through a number of examples similar to those you might find on the ap calculus bc exam.<\/p>\n
what makes a series alternating<\/strong> is the pattern of its signs<\/em>. positive terms alternate with negative terms forever. the first term may be either positive or negative.<\/p>\n so, if b<\/em>1<\/sub>, b<\/em>2<\/sub>, b<\/em>3<\/sub>, b<\/em>3<\/sub>, etc., are positive, then both of the following are alternating series.<\/p>\n <\/p>\n for example, the following series is alternating.<\/p>\n <\/p>\n here’s another example. notice again how the factor of (-1)n<\/sup><\/em> switches the sign.<\/p>\n <\/p>\n here is one that is not easy to tell is alternating. in fact, it’s not obvious until you work out the value of each term. remember your unit circle!<\/p>\n <\/p>\n there is actually a very simple test for convergence that applies to many of the series that you’ll encounter in practice.<\/p>\n suppose that σan<\/sub><\/em> is an alternating series, and let bn<\/sub><\/em> = |an<\/sub><\/em>|. then the series converges if both of the following conditions hold.<\/p>\n <\/li>\n<\/ol>\n basically, if a series alternates, then as long as the terms get closer to zero, there must be a finite sum. think of a bouncing ball. each up bounce is a positive term, and each downward return is a negative term. if the next bounce is always smaller than the previous one, then eventually the ball will come to rest.<\/p>\nalternating series test<\/h2>\n
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