techniques for finding an expression for geometric seqeunces  TOPIC_SOLVED

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techniques for finding an expression for geometric seqeunces

Postby rogermiranda on Thu Jul 29, 2010 2:56 pm

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.
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Re: techniques for finding an expression for geometric seqeu  TOPIC_SOLVED

Postby king&i on Thu Jul 29, 2010 10:24 pm

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.
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