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Photo by Vickie Kelly, 2008. Greg Kelly, Hanford High School, Richland, Washington. 8.1: Sequences. Craters of the Moon National Park, Idaho. A sequence is a list of numbers written in an explicit order. n th term.
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Photo by Vickie Kelly, 2008 Greg Kelly, Hanford High School, Richland, Washington 8.1: Sequences Craters of the Moon National Park, Idaho
A sequence is a list of numbers written in an explicit order. nth term Any real-valued function with domain a subset of the positive integers is a sequence. If the domain is finite, then the sequence is a finite sequence. In calculus, we will mostly be concerned with infinite sequences.
Example: A sequence is defined explicitly if there is a formula that allows you to find individual terms independently. To find the 100th term, plug 100 in for n:
Example: A sequence is defined recursively if there is a formula that relates an to previous terms. We find each term by looking at the term or terms before it: You have to keep going this way until you get the term you need.
An arithmetic sequence has a common difference between terms. Example: Arithmetic sequences can be defined recursively: or explicitly:
An geometric sequence has a common ratio between terms. Example: Geometric sequences can be defined recursively: or explicitly:
If the second term of a geometric sequence is 6 and the fifth term is -48, find an explicit rule for the nth term. Example:
ENTER Sequence Graphing on the Ti-89 Change the graphing mode to “sequence”: MODE Graph……. 4
Y= alpha Use the key to enter the letter n. Example: Plot Leave ui1 blank for explicitly defined functions.
WINDOW GRAPH
Y= alpha Use the key to enter the letters u and n. The previous example was explicitly defined. Now we will use a recursive definition to plot the Fibonacci sequence. Enter the initial values separated by a comma (even though the comma doesn’t show on the screen!)
WINDOW Enter the initial values separated by a comma (even though the comma doesn’t show on the screen!)
WINDOW GRAPH You can use F3 Trace to investigate values.
TBLSET TABLE We can also look at the results in a table. Scroll down to see more values.
TABLE Scroll down to see more values.
Does converge? You can determine if a sequence converges by finding the limit as n approaches infinity. The sequence converges and its limit is 2.
Absolute Value Theorem for Sequences If the absolute values of the terms of a sequence converge to zero, then the sequence converges to zero. Don’t forget to change back to function mode when you are done plotting sequences. p