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**The sum of the infinite and finite geometric sequence**

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**The sum of the first n terms of a sequence is represented by summation notation.**

upper limit of summation lower limit of summation index of summation 2

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**The sum of a finite geometric sequence is given by**

= ? n = 8 a1 = 5

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**If |r| < 1, then the infinite geometric series**

The sum of the terms of an infinite geometric sequence is called a geometric series. If |r| < 1, then the infinite geometric series a1 + a1r + a1r2 + a1r a1rn has the sum

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**Example: Find the sum of**

The sum of the series is

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**Convergent and Divergent Series**

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**Convergent and Divergent Series**

If the infinite series has a sum, or limit, the series is convergent. If the series is not convergent, it is divergent.

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**Ways To Determine Convergence/Divergence**

1. Arithmetic – since no sum exists, it diverges 2. Geometric: If |r| > 1, diverges If |r| < 1, converges since the sum exists 3. Ratio Test (discussed in a few minutes)

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Example Determine whether each arithmetic or geometric series is convergent or divergent. 1/8 + 3/20 + 9/ / r=6/5 |r|>1 divergent Arithmetic series divergent /5 + 13/ r=1/5 |r|<1 convergent

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Other Series When a series is neither arithmetic or geometric, it is more difficult to determine whether the series is convergent or divergent.

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Ratio Test In the ratio test, we will use a ratio of an and an+1 to determine the convergence or divergence of a series. Leading coefficient is a Review: Leading coefficient is d Denominator degree is greater

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**Test for convergence or divergence of:**

Since this ratio is less than 1, the series converges.

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**The ratio of the leading coefficients is 1**

Test for convergence or divergence of: The ratio of the leading coefficients is 1 Since this ratio is less than 1, the series converges.

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**Test for convergence or divergence of:**

Coefficient of n2 is 1 Since this ratio is 1, the test is inconclusive. Coefficient of n2 is 1

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Example Use the ratio test to determine if the series is convergent or divergent. 1/2 + 2/4 + 3/8 + 4/ Since r<1, the series is convergent.

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Example Use the ratio test to determine if the series is convergent or divergent. 1/2 + 2/3 + 3/4 + 4/ Since r=1, the ratio test provides no information.

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Example Use the ratio test to determine if the series is convergent or divergent. 2 + 3/2 + 4/3 + 5/ Since r=1, the ratio test provides no information.

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Example Use the ratio test to determine if the series is convergent or divergent. 3/4 + 4/16 + 5/64 + 6/ Since r<1, the series is convergent.

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Example Use the ratio test to determine if the series is convergent or divergent. Since r<1, the series is convergent.

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Example Use the ratio test to determine if the series is convergent or divergent. Since r>1, the series is divergent.

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