# Homework Help: General Phase Shift Question

1. May 26, 2012

### smashbrohamme

Find the phase shift of a function.

Y=-5sin(x-pie/2)

The Phase shift is (pie/2)/1 which equals to pie/2. The correct answer is units to the right though..which is where I need clarification on.

My book said if phi is less than 0, it is too the left.. being -pie/2 wouldn't this indicate to the left?

Another example.

y=4cos(x+pie/2) once again phase shift is pie/2...but it is units to the left...units to left indicates phi...which is pie in this case..is negative...how is that possible?

It is easy to remember if it has a plus sign..it is units to the left...
negative sign ends up being units to the right...I just don't understand and if I don't truly understand than I won't remember it long term.

Thanks for your help.

2. Relevant equations

3. The attempt at a solution

2. May 26, 2012

### SammyS

Staff Emeritus
Does your book say something like:
For
$\sin(x-\phi)\,,$​
if $\phi$ is positive then the shift is to the right,

if $\phi$ is negative then the shift is to the left .​

?

If that's the case, then your $\phi$ is π/2, which is positive.

3. May 26, 2012

### smashbrohamme

ah, so they are factoring in that your equation sin(w-phi) can make two negatives into a positive...

4. May 26, 2012

### SammyS

Staff Emeritus
Yes.