# 9.5 Testing Convergence at Endpoints Greg Kelly, Hanford High School, Richland, Washington The original Hanford High School, Hanford, Washington

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9.5 Testing Convergence at Endpoints Greg Kelly, Hanford High School, Richland, Washington The original Hanford High School, Hanford, Washington Slide 2 Remember: The series converges if. The series diverges if. The test is inconclusive if. The Ratio Test: If is a series with positive terms and then: Slide 3 This section in the book presents several other tests or techniques to test for convergence, and discusses some specific convergent and divergent series. Slide 4 The series converges if. The series diverges if. The test is inconclusive if. Nth Root Test: If is a series with positive terms and then: Note that the rules are the same as for the Ratio Test. Slide 5 example: ? Slide 6 Indeterminate, so we use LHpitals Rule formula #104 formula #103 Slide 7 example: it converges ? Slide 8 another example: it diverges Slide 9 Remember that when we first studied integrals, we used a summation of rectangles to approximate the area under a curve: This leads to: The Integral Test If is a positive sequence and where is a continuous, positive decreasing function, then: and both converge or both diverge. Slide 10 Example 1: Does converge? Since the integral converges, the series must converge. (but not necessarily to 2.) Slide 11 p-series Test converges if, diverges if. We could show this with the integral test. If this test seems backward after the ratio and nth root tests, remember that larger values of p would make the denominators increase faster and the terms decrease faster. Slide 12 the harmonic series: diverges. (It is a p-series with p=1.) It diverges very slowly, but it diverges. Because the p-series is so easy to evaluate, we use it to compare to other series. Slide 13 Limit Comparison Test If and for all ( N a positive integer) If, then both and converge or both diverge. If, then converges if converges.If, then diverges if diverges. Slide 14 Example 3a: When n is large, the function behaves like: Since diverges, the series diverges. harmonic series Slide 15 Example 3b: When n is large, the function behaves like: Since converges, the series converges. geometric series Slide 16 Alternating Series The signs of the terms alternate. Good news! example: This series converges (by the Alternating Series Test.) If the absolute values of the terms approach zero, then an alternating series will always converge! Alternating Series Test This series is convergent, but not absolutely convergent. Therefore we say that it is conditionally convergent. Slide 17 Since each term of a convergent alternating series moves the partial sum a little closer to the limit: Alternating Series Estimation Theorem For a convergent alternating series, the truncation error is less than the first missing term, and is the same sign as that term. This is a good tool to remember, because it is easier than the LaGrange Error Bound. Slide 18 There is a flow chart on page 505 that might be helpful for deciding in what order to do which test. Mostly this just takes practice. To do summations on the TI-89: becomes F34 Slide 19 To graph the partial sums, we can use sequence mode. MODE Graph.4 ENTER Y= WINDOW ENTER GRAPH Slide 20 To graph the partial sums, we can use sequence mode. MODE Graph.4 ENTER Y= WINDOW ENTER GRAPH Table Slide 21 To graph the partial sums, we can use sequence mode. MODE Graph.4 ENTER Y= WINDOW ENTER GRAPH Table

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