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