# Nth Term Formula Sequence

1. Mar 25, 2013

### whatlifeforme

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. Mar 25, 2013

### SammyS

Staff Emeritus
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.

3. Mar 26, 2013

### whatlifeforme

please explain how i would implement cosine or sine.

4. Mar 26, 2013

### sudu.ghonge

Try sin (n*pi/2) and add integer constants to n to shift the series.

5. Mar 26, 2013

### whatlifeforme

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

6. Mar 26, 2013

### SammyS

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

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