# Homework Help: Convert harmonic equation to polar form

1. Jan 15, 2008

### ssb

1. The problem statement, all variables and given/known data

Convert
$$cos(7 t) + sin(7 t)$$
into polar form of
$$A cos(\omega_0 t - \delta)$$

This is a review problem where once we convert this to polar form we are to give amplitude, period and delay (shift). I can answer this question if someone can point me to a website tutorial that tells the process of converting this problem. I really dont expect someone to answer this for me because I need to learn how to do it on my own.

3. The attempt at a solution

I have not made an attempt as of yet, however i know there is a trig identity
cos(x)cos(y) + sin(x)sin(y) = cos(x-y)

I was given this advice BUT I dont know what to do because:
cos(7)cos(t) doesnt equal cos(7t) .... right?

Last edited: Jan 15, 2008
2. Jan 15, 2008

### rock.freak667

Let $Acos(\theta-\delta)=cos(7t)+sin(7t)$ then just equate and solve

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