Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Ratio test, why does the (-1)^(n+1) disappear?

  1. Dec 1, 2004 #1
    In the book while doing the ratio test:

    as n --> infinity

    why do they just have (-1)^(n+1) just disappear in the next step, since it oscillates between -1 and 1, I don't understand how u could just make it disappear in computations. Isn't the limit as n -> infinity , equal to D.N.E.?
     
  2. jcsd
  3. Dec 1, 2004 #2
    I believe the ratio test tests the absolute value of |An+1 / An|. so the (-1)^n and (-1)^n+1 will just be one, so u can just take it out.
     
  4. Dec 1, 2004 #3
    crap lol, i didn't even think of that. THanks cyrus, u da man!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook