# Homework Help: Time Domain Functions to Frequency Domain

1. Nov 23, 2008

### CaptProton987

How do you convert functions from the time domain, to the frequency domain
For example: cos(250t + 30degrees) is what in the frequency domain?
Are there some general steps I can follow to do this?

2. Nov 23, 2008

### Matt1234

Your going to need your laplace transformations table.
Basically you can split 250t do that part which would work out to:

for the 250 part its entry #2 in the table

F(S) = (250/s ^2) + L(30 deg)

The L above stands for laplace transform i still left that part in the time domain. I would convert 30 deg. to radians which is a constant and then use that number over s. That is entry number 1 in the table.

3. Nov 23, 2008

### Redbelly98

Staff Emeritus
The technique for doing that is the Fourier Transform. Try a google search on that, as well as "Fourier Series". These might be in your course textbook also.

4. Nov 23, 2008

### Redbelly98

Staff Emeritus
I think Laplace transforms may be overkill hill. The OP is just looking for the frequency-domain representation, i.e. the frequency spectrum.

5. Nov 23, 2008

### Matt1234

Your correct, no argue from here, im a 3rd year Electrical engineering student new to this site and intend on staying around. :) Great palce, and sorry to go off topic.