anonymous
  • anonymous
i need some help with infinite series! i don't understand :(
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
what in particular? convergence?
anonymous
  • anonymous
yeah, the homeworks says to "find exact values for the first four partial sums, find a closed form for the nth partical sum, and determine whether the series converges by calculating the limit of the nth partial sum. if the series converges, then state its sum" i have a feeling it's easy and i'm just misunderstanding the basics
anonymous
  • anonymous
the first question is " 2+2/5+2/5^2+...+ 2/ 5^k-1"

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anonymous
  • anonymous
ok, that is actually a geometric series, so for the limit of the sum, use the finite geometric series formula
anonymous
  • anonymous
\[\sum_{0}^{k-1}2*(1/5)^n\]
anonymous
  • anonymous
finite geometric sum formula is a(1-r^n)/(1-r) where r is ratio and a is 1st term (in this case a=2 and r=1/5
anonymous
  • anonymous
when you take the limit, since r is less than 1, the r^n term is gonna get smaller and smaller and eventually disappear, which leaves the much easier formula of just a/(1-r) or in this case 2/(1-1/5)=2/(4/5) multiply by reciprocal of the bottom and reduce and you should get 5/2
anonymous
  • anonymous
wow! thanks for saving my life. you're the best :)

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