# Basic trig phase question *sorry*

by Rudibot
Tags: basic, phase, trig
 P: 10 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!
P: 606
 Quote by 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!

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

DonAntonio
 Math Emeritus Sci Advisor Thanks PF Gold P: 38,706 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.

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