1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Problem on induction

  1. Oct 15, 2011 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    Show that Sn=(-1)^n(n+1)

    3. The attempt at a solution

    S(n+1)=Sn+(-1)^(n+1)*(2n+3) = (-1)^n*(n+1)+ (-1)^(n+1)*(2n+3)
    S(n+1)= (-1)^(n+1)*[(2n+3)-(n+1)] (because (-1)^(n+1)= - (-1)^n )

    is that correct proof
    Last edited: Oct 15, 2011
  2. jcsd
  3. Oct 15, 2011 #2


    User Avatar
    Science Advisor

    Well, you haven't shown that it is true for n= 1, so, no. But that is easily fixed.
  4. Oct 15, 2011 #3
    i did that before doing the work and for n=1 it came out to equal -3 and i also had to count S2 and S3 and i got 5 for S2 and -7 for S3.

    But my proof is fine right?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook