# Homework Help: Another change in unit vectors (d(r-hat)/d(theta)) in Cylindrical

1. Nov 18, 2011

### khfrekek1992

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

Does anyone know what d(r-hat)/d(theta) in Cylindrical coordinates is?

2. Relevant equations

3. The attempt at a solution

I'm pretty sure its -(theta-hat) but I'm not sure, any help?

Thanks so much

2. Nov 18, 2011

### khfrekek1992

so theta is moved over by d(theta) shifting over r-hat and theta-hat.. What would d(r-hat)/d(theta) be?

3. Nov 18, 2011

### khfrekek1992

anyone? :)

4. Nov 18, 2011

### I like Serena

Hi khfrekek1992!

$${d\hat r \over d\theta} = \hat \theta$$

If you draw $\hat r$ for 2 angles, you'll see that the vector-difference between them points in the direction of $\hat \theta$.
Its (approximate) length is $d\theta$.

5. Nov 18, 2011

### khfrekek1992

Oh! I see how you get that now.. Thanks so much! That helps a ton :D