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Nth Term Formula Sequence

  1. Mar 25, 2013 #1
    1. The problem statement, all variables and given/known data
    I am trying to solve this problem and need help with one aspect.


    2. Relevant equations
    sequence: 0,-1,0,1 -- repeated.


    3. The attempt at a solution
    How do I make every 4th term of the sequence a negative number?

    for instance i have: (1 + (-1)^n)/2 but i don't know how to alternative the -1 term in.
     
    Last edited: Mar 25, 2013
  2. jcsd
  3. Mar 25, 2013 #2

    SammyS

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    What functions are you willing to use.

    This can easily be done with sine or cosine .

    You can probably come up with some solution using the "mod" function.
     
  4. Mar 26, 2013 #3
    please explain how i would implement cosine or sine.
     
  5. Mar 26, 2013 #4
    Try sin (n*pi/2) and add integer constants to n to shift the series.
     
  6. Mar 26, 2013 #5
    then you are going 1, 0, -1, 0. (so if i put sin(pi/2 + npi/2) into the ratio, then i multiply by negative 1 the correct number of times, but what about the zeros? sinx=0 ---> v(sinx) = 0
     
  7. Mar 26, 2013 #6

    SammyS

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    So, it appears you're starting with n = 1 .

    Why is it that you say that [itex]\displaystyle \ -\,\sin\left(\frac{\pi}{2}+\frac{n\pi}{2}\right)\ [/itex] doesn't work ?
     
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