 # Geometric Sequences A Geometric Sequence is n a

• Slides: 12 Geometric Sequences A Geometric Sequence is n a sequence of numbers in which each term is formed by multiplying the previous term by the same number or expression. The consecutive terms have a common ratio. 1, 3, 9, 27, 81, 243, . . . The terms have a common ratio of 3. Geometric Sequence Example Is the following sequence geometric? 4, 6, 9, 13. 5, 20. 25, 30. 375… n Yes, the common ratio is 1. 5 Geometric Sequence n To find any term in a geometric sequence, use the formula an = a 1 rn– 1 where r is the common ratio. Example Find the twelfth term of the geometric sequence whose first term is 9 and whose common ratio is 1. 2. an = a 1 rn– 1 a 1 = 9 r = 1. 2 a 9 = 9 • 1. 211 a 12 = 66. 87 n To find the sum of a geometric series, we can use summation notation. Example Which can be simplified to: Evaluate the sum of: n Convert this to = 7. 49952 Series Series Series n Definition: A series is a partial sum of the first n terms of a sequence. General term: nth partial sum: Sn =. n nth partial sum of arithmetic sequence: n Example: nth partial sum of an = -1 + 5 n. n Sn = Series n nth partial sum of geometric sequence: n Sum of an infinite geometric sequence: n n If |r|<1, n If |r| 1, a geometric series has no infinite sum. Example: Series n Product notation: