How do you find the sum of the infinite geometric series given $a_1=18$ and r=-1.5?

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Answer 1 · 2017-01-21T20:41:06

This Geometric series will not have a "sum", since the $|-1.5|$ = 1.5 which is greater than 1.

This means that the terms, although alternating positive and negative, will grow larger and larger, thus producing an infinite sum.

If the $|r| <1$ , you can then compute the sum with the formula: $S_oo=(a_1)/(1-r)$ .

How do you find the sum of the infinite geometric series given a_1=18a_1=18 and r=-1.5?