Once i find the radius of convergence, how do i find the interval of convergence?

  • Thread starter mr_coffee
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  • #1
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Hello everyone, i'm confused (as usual). I think i found the radius of convergence but then waht do i do to find the interval on which it converges?

The directions says:
Find all the values of x such that the given series would converge.
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/70/aaf16ffcdb10d6976585856b5dafca1.png [Broken]
The series is convergent
from x = , left end included (enter Y or N):
to x = , right end included (enter Y or N):

Here is my work:
http://img90.imageshack.us/img90/6637/lastscan5ox.jpg [Broken]


Any help would be great! thankss!
 
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Answers and Replies

  • #2
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OKay i had to of messed up finding the radius of convergence. I looked at a tutoiral and it should be right...
I got
(-7,7); for the interval, which was wrong though. Can you see where i screwed it up? it should be open brackets i got that part right

Okay i did it again, and i tried (-14,14), now i have 75% of the question rgiht, so either -14 is wrong or 14 is wrong but i don't see how u can get any other number then that.
if u have
|(x-7)/7| < 1

and
|(x-7)/7| > 1
 
Last edited:
  • #3
HallsofIvy
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Why did [itex]\left|\frac{x-7}{7}\right|< 1[/itex] become x-7< 7??
Shouldn't it be |x-7|< 7? And doesn't that mean that -7< x- 7< 7?
So that 0< x- 7< 14?
 
  • #4
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Thanks Ivey ur the man! i forgot all about that rule!
w00t.
 

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