Posted by **purple1** on Saturday, March 20, 2010 at 8:14pm.

find the sum of each of the following infinite series, if no sum, write no sum.

9-3+1-1/3+1/9...

1/2+1+2+4...

- math -
**Reiny**, Saturday, March 20, 2010 at 8:40pm
S_{∞} = a/(1/r) where │r│ < 1

in the first,

a = 9, r = -1/3

so sum = 9/(1 - (-1/3)) = 6.75 or 27/4

For the second one, there is no sum, since the series diverges.

notice r = 2, so it does not satisfy the condition for the formula.

- math -
**purple1**, Saturday, March 20, 2010 at 8:44pm
Thank you.

- typo - math -
**Reiny**, Saturday, March 20, 2010 at 8:49pm
I just notice a typo in my formula, should of course be

a/(1-r) where │r│ < 1

I did use it correctly in the calculations

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