Originally Posted by

**davet101** Hi all,

The question I have is:

Calculate between 0 and 2.25s, the times at which the waveforms:

v=3cos3t and v=4sine6t cross.

So far I have calculated the time periods for both waveforms:

For Cosinewave: T = 2\pi /3 s

as v=3cos(3t) or v = 3cos(\omega t) where \omega = 2\pi f

Therefore: \omega = 2\pi /T = 3

So T = 2\pi /3

For Sinewave: T = 2\pi /6 s

as v=4sine(6t) or v = 4sine(\omega t) where \omega =2\pi f

Therefore: \omega = 2\pi /T = 6

So T = 2\pi /6

So it is evident that my sinewave is exactly twice the frequency of my Cosinewave, and

obviously what I want to achieve is to calculate the times where 3cos3t = 4sin6t.

I believe its required to use trigonometrical identoties to solve this problem from this point, but what approach/method to take I have no idea at this time.

Any help on this is greatly appriciated.

Thanks,

Dave

P.S: I am aware that I'm asking a question on my first post, but I intend to be of use to others here, where possible anyway!