## techniques for finding an expression for geometric seqeunces

Complex numbers, rational functions, logarithms, sequences and series, matrix operations, etc.
rogermiranda
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Joined: Fri Apr 30, 2010 6:01 pm
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### techniques for finding an expression for geometric seqeunces

I know that there are certain techniques and steps on finding expressions for linear and quadratic sequences. But can someone give me a technique or set of steps that I can use to figure out expressions for geometric sequences?
For example, I have the geometric sequence 4,8,16,32,64.... The common ratio is 2. The expression to generate this sequence is 2^n+1. But I would like to learn the steps needed to figure out the expression. Can someone please help.

king&i
Posts: 23
Joined: Sat Mar 07, 2009 5:13 pm

### Re: techniques for finding an expression for geometric seqeu

They've got a lesson here: http://www.purplemath.com/modules/series3.htm

You can use the fomrulas. Like for 4,8,16,32,64, you have r=2, a=4. then an=a*2n-1. And a=4=22, so an=(22)(2n-1)=22+n-1=2n+1.