SOLUTION: show that the following series converges absolutely for |x|<1 and compute the sum. f(x)=1-x-x^2+x^3-x^4-x^5+x^6-x^7-x^8+... The hint we were given was to write f(x) as the sum of

Algebra ->  Sequences-and-series -> SOLUTION: show that the following series converges absolutely for |x|<1 and compute the sum. f(x)=1-x-x^2+x^3-x^4-x^5+x^6-x^7-x^8+... The hint we were given was to write f(x) as the sum of      Log On


   



Question 1074919: show that the following series converges absolutely for |x|<1 and compute the sum.
f(x)=1-x-x^2+x^3-x^4-x^5+x^6-x^7-x^8+...
The hint we were given was to write f(x) as the sum of 3 geometric series with a common ratio of x^3

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!

is one of the infinite geometric series hinted at.
The first term is 1 and the common ratio is x%5E3 .
The other two series are
,
with first term -x , and
,
with first term -x%5E2 .
Geometric series with a first term b,
and common ratio r such that abs%28r%29%3C1
converge to b%2F%281-r%29 .
Since abs%28x%29%3C1 means abs%28x%5E3%29%3Cabs%28x%29%3C1,
those 3 series converge to the sums shown above.
Since each series converges, so does its sum.
f%28x%29=S%5B1%5D%2BS%5B2%5D-S%5B3%5D=%281-x-x%5E2%29%2F%281-x%5E3%29 .