Advanced Math Topics Mrs. Mongold Geometric Sequences Advanced Math Topics Mrs. Mongold
Reminder: Arithmetic Sequence Definition: Sequence in which the difference between any term and the term before it is a constant. i.e. you are adding or subtracting the same number each time Example: 2, 4, 6, 8, … You are adding 2 to each term to get the next 10, 9, 8, 7, … You are subtracting 1 from each term to get the next
Common Difference Definition: Example: The value of an – an-1 2, 4, 6, 8, … 4 – 2 = 2 6 – 4 = 2 8 – 6 = 2 d= 2
Geometric Sequence Definition: Example: Sequence in which the ratio of any term to the term before it is a constant. i.e. each term is multiplied or divided by the same number Example: 2, 4, 8, 16, … You multiply the previous term by 2 to get the next number 81, 27, 9, 3, … You divide each term by 3 to get the next number
Common Ratio The value of an divided by an-1 Example: 2, 4, 8, 16, … 4/2 = 2 8/4 = 2 16/8 = 2 So common ratio r =2 If the pattern is dividing the common ratio is a fraction!!!
Geometric Sequence 0.05, 0.25, 1.25, 6.25, … Explicit Formula an=a1rn-1 Pattern is previous term times 5 so r = 5 an=.05 (5)n-1 Recursive Formula an=(an-1)r Pattern is previous term times 5 so r = 5 an =(an-1)5 an=5(an-1)
Examples 1,-5, 25, -125, … -4, -8/3, -16/9, -32/27…
More Examples a1 = 4, r=3
More Examples a1 = 8, r= ½
More Examples a1 = 25, r= -5
More Examples
More Examples 100, 20, 4, 0.8, …
More Examples 1, 3, 6, 10, …
More Examples 12, 17, 22, 27, …
More Examples 0, 1, -1, 0, 1, -1 …
More Examples 25, 22, 19, 16, …
More Examples
Homework Arithmetic Sequences HW #2 Geometric Sequences HW #3