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Hello everyone.
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So in this question we have given three alternating series and we have to check which alternating series can be used to show convergence using alternating series test.
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So now let us understand first that what is alternating series test? alternating series test.
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So the alternating series test says that if limit n -tenthens.
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To infinity absolute value of a .n.
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Is equal to zero and series is decreasing, that is, absolute value of a .n plus one should be less than equal to absolute value of a .n.
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So if these two conditions satisfies by alternating series, then we can say that alternating series is a convergent.
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So now we will answer our question one by one.
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So our first question is, 4 minus 1 divided by 9 plus 1 minus 1 divided by 81 plus 1 divided by 4 minus 1 divided by 729 plus so on plus 8 divided by 2 power n minus 1 divided by 3 power n plus 1 and so on.
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So this is our alternating series.
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So now in this series, here we can write absolute value of a1, that is first term, is equal to 4, then absolute value of a2 is equal to 1 divided by 9, then absolute value of a3 is equal to 1, absolute value of a4 from the series is equal to 1 divided by 81.
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Similarly, absolute value of a5 is equal to 1 divided by 4 and so on.
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So now as we can see here that absolute value of a1 is greater than absolute value of a2.
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Then absolute value of a2 is less than absolute value of a3.
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Then absolute value of a3 is greater than absolute value of a4.
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Then absolute value of a4 is less than absolute value of a5.
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So therefore we can say that absolute value of an is not monotonically decreasing.
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And if one condition fails, then no need to find other condition.
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So therefore, we can say that...