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Geometric Series Objectives. 1. 2. Evaluate a finite and infinite geometric series. Understand the difference between convergence and divergence, and identify. Evaluating a Finite Geometric Series. Sum of a Finite Geometric Series
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Geometric Series Objectives 1. 2. Evaluate a finite and infinite geometric series. Understand the difference between convergence and divergence, and identify.
Evaluating a Finite Geometric Series Sum of a Finite Geometric Series The sum Snof a finite geometric series a1 + a2 + a3 + . . . an is where a1is the 1st term, r is the common ratio, & n is the # of terms.
Example 1: Using the Geometric Series Formula Use the formula to evaluate the series 3 + 6 + 12 + 24 + 48 + 96. The first term is ___, and there are ___ terms in the series. 3 6 The common ratio is = 2 So a1 = ___, r = ___, and n = ___. 3 2 6 189
Example 2: Real-World Connection Financial Planning: In March, Larry, Moe and Curly start saving for a vacation at the end of August. The Stooges expect the vacation to cost $1,375. They start with $125. Each month they plan to deposit 20% more than the previous month. Will they have enough $ for their trip? Write the geometric series formula. Sn = Total amount to be saved. a1 = $125 r = 1.2 n = 6 $1,243.75
255256 Examples 1 & 2: Practice Evaluate the finite series for the specified number of terms. 1. 1 + 2 + 4 + . . . ; n = 8 2. 3 + 6 + 12 + . . . ; n = 7 3. -5 – 10 – 20 – . . . ; n = 11 255 381 -10,235 4.
Infinite Geometric Series: Convergence vs. Divergence In some cases, you can evaluate an infinite geometric series. When │r│< 1, the series converges (i.e. gets closer and closer to the sum S). When │r│≥ 1, the series diverges (i.e. it approaches no limit).
∞ 5(2)n-1 n = 1 Example 3: Determining Divergence & Convergence Decide whether each infinite geometric series diverges or converges. State whether the series has a sum. A. B. a1 = 1 a1 = 5 a2 = -⅓ a2 = 10 r = -⅓ 1 = -⅓ r = 10 5 = 2 Since │r │ < 1, the series converges & has a sum. Since │r │ > 1, the series diverges & does not have a sum.
Example 3: Practice Decide whether each infinite geometric series diverges or converges. State whether the series has a sum. 5. 6. 7. 8. 9. converges; has a sum converges; has a sum converges; has a sum diverges; no sum diverges; no sum 4 + 2 + 1 . . . 6 + 18 + 54 + . . . 1 - 1 + 1 - . . . ¼ + ½ + 1 + 2 . . .
Sum of an Infinite Geometric Series An infinite geometric series with │r│ < 1 converges to the sum of where a1is the 1st term, r is the common ratio. You can use the sum formula to evaluate some infinite geometric series.
Example 4: Real-World Connection 27mm The length of the outside shell of each closed chamber of a chambered nautilus is 0.9 times the length of the larger chamber next to it. What is the best estimate for the total length of the outside shell for the enclosed chambers? S1 = 27 = 270 mm
92 95 Example 4: Practice Evaluate each infinite geometric series. 10. 11. 12. 1.1 – 0.11 + 0.011 - . . . 1