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Geometric Sequences and Series. Sections 11.3 and 11.5. Review Terms. Sequence An ordered list of numbers Series The sum of the terms of a sequence Term A specific number in a sequence Arithmetic Sequence A sequence of numbers where the difference between consecutive terms is constant
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Geometric Sequences and Series Sections 11.3 and 11.5
Review Terms • Sequence • An ordered list of numbers • Series • The sum of the terms of a sequence • Term • A specific number in a sequence • Arithmetic Sequence • A sequence of numbers where the difference between consecutive terms is constant • Geometric Sequence • A sequence of numbers where the ratio between consecutive terms is constant
Geometric Equations Recursive Closed (or explicit) This equation refers to other terms in the sequence. an = an–1 ∙ r This equation allows you to find any term in the sequence directly. an = a1 ∙r n–1
Geometric sequence Determine if the following sequence is geometic. If it is, write both types of formulas. • 1, –2, 4, –8, … Yes this is. an = an–1∙ (–2) and an = (–2)n–1 • 1, 2, 3, 4, … No this is not geometric. The ratios keep changing.
Practice Determine if each of the following sequences is geometric. If it is write both types of formulas. • 7, 0.7, 0.07, 0.007, … • 10, 15, 22.5, 33.75, … • 1/2, 1/4, 1/6, 1/8, … Yes. an = an–1•(0.1) or an = 7 (0.1)n–1 Yes. an = an–1 •(1.5) or an = 10 (1.5)n–1 No, there is not a common ratio.
Finite Geometric Series • This is used for finite geometric series. • n is the number of terms • a1 is the first term in the sequence • r is the common ratio between consecutive terms
Finite Series Practice Evaluate the following series for the given number of terms: • 1 + 2 + 4 + …; S8 S8= (1 (1 – 28))/(1 – 2) = 255
Finite Series Practice Evaluate the following series for the given number of terms: • 1 + 2 + 4 + …; S8 S8= (1 (1 – 28))/(1 – 2) = 255 S5= (7 (1 – (– 5)5))/(1 – (–5)) = 3647
Infinite Geometric Series • This is used for infinite geometric series • The variables are the same as for the finite series • This can be used to convert repeating decimals to fractions
Infinite Series Practice Evaluate the following geometric series, or find the fraction equivalent for the given infinite repeating decimal. 1.22222… • 0.222222… a1 = 0.2, r = 0.1 S = 2/9
Practice Convert the following infinite repeating decimals to fractions. • 0.42857142857142… • 0.066666666… • 0.2727272727… 3/7 1/15 3/11