1. Pre Calculus 11 Section 1.5 Infinite Geometric Series

2. I) What is an Infinite Geometric Series?
A Geometric series with an infinite number of terms
If the common ratio is greater than 1, each term will get bigger and the sum will soon add up to infinity
Note: Any infinite G.S. with a common ratio then the sum will add up to infinity
Most infinite G.S. in sect. 1.5 will have a common ratio between -1 and 1
Each term in the series will get smaller
Eventually some terms will become so small such that adding them will be insignificant, like adding zero
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3. Ex: Indicate whether if the series is convergent or divergent?
These values are so small such that adding them will be insignificant!!
When the ratio is the infinite G.S. is “convergent” meaning it will eventually converge/add to a fixed value
When the ratio is the infinite G.S. is “divergent” meaning it will add to infinity
Ex: Indicate whether if the series is convergent or divergent?
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4. II) Formula for the SUM of an Infinite G.S.
If the Ratio is bigger than 1, the sum will be positive infinity
If the ratio is smaller than -1, the sum will be negative infinity
If the Ratio is between 1 and -1, the sum can be obtained through a formula:
Formula for the sum of a G.S. with “n” terms
If there are infinite terms, then “n” will be infinity
Since
the value of
will be zero
The equation will only apply if
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5. Ex: Find the sum of the Infinite G.S.
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6. INVESTIGATE: Given the Geometric series: What happens to the sum if there are more terms?
If you have more terms, the sum gets closer to 1
If there are infinite number of terms the sum will be equal to 1

7. Ex: The common ratio of an infinite geometric series is 0. 75
Ex: The common ratio of an infinite geometric series is If the sum of all the terms converges to 20, find the first term.
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8. Given the following infinite geometric sequence, what should the value of “r” be so that the sum will be 20?
The series must be converging
So the value of “r” must be between -1 and 1
The answer must be r = 0.80
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9. Ex: a movie in a theatre generate $250,000 in revenue in the first month of its showing. Each month, sales from that movie drop by 15%. If the movie is shown for a long time, what is the total revenue generated?
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10. Challenge: Given the following infinite geometric series, What value of “x” will the series converge?
To ensure that the series is converging, only the common ratio is required
The common ratio is “3x” and this value must be between 1 and – 1
So if the series is converging , then “x” must be greater than – 1/3 and less than 1/3

11. HW:
Assignment 1.5
Pg. 63 #1 – 18 (Odd Numbers)