Discover the Sum of an Infinite Series: A Refresher

duki
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Homework Statement



Find the sum of the infinite series: 405-270+180-120+80...

Homework Equations



??

The Attempt at a Solution



I know there's a formula for this but I can't remember it. Could someone refresh my memory?
 
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You'll need to start by finding the pattern between successive terms in the series... call the first term a_0=405 , the 2nd term a_1=-270 etc... so that the series can be represented as:

405-270+180-120+80 \ldots=a_0+a_1+a_2+a_3+a_4 \ldots=\sum_{n=0}^{\infty} a_n

There should be any easy to spot relationship between terms in the series...can you spot it?
 
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