Basic trig phase question *sorry*

Rudibot

I'm a bit rusty..

I have a cosine
y = cos(2*pi*f*t)
If I want to advance the cosine by say 90 degrees
y = cos(2*pi*f*t + pi/2)

but..
this waveform has f cycles per 2*pi*t..so won't I be advancing the phase by f*pi/2?
someone pls straigthen me out - I'm working with Matlab indexes and I'm getting confused!

DonAntonio

I'm not really sure what're you asking, but [itex]\,\,\displaystyle{\cos \left(\alpha+\frac{\pi}{2}\right)=-\sin (\alpha)}\,\,[/itex]

DonAntonio

HallsofIvy

cos(2*piZ*f*t+ pi/2) is different from cos(2*pi*f(t+ pi/2)). The first just translates the wave by pi/2, the second translates by pi^2*f.