# Nth Term Formula Sequence

## Homework Statement

I am trying to solve this problem and need help with one aspect.

## Homework Equations

sequence: 0,-1,0,1 -- repeated.

## 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:

SammyS
Staff Emeritus
Homework Helper
Gold Member

## Homework Statement

I am trying to solve this problem and need help with one aspect.

## Homework Equations

sequence: 0,-1,0,1 -- repeated.

## 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.
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.

please explain how i would implement cosine or sine.

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

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

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