# Homework Help: A vector calculus proof question

1. Jan 8, 2013

### physics2000

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

The image contains the problem statement and all relevant equations. I have no idea what to do, this is all very new to me...plus the hint doesnt make sense to me.

2. Jan 8, 2013

### Dick

I think they just want you to show that the dot product of grad(∅) with dr gives you the expression for d(∅) in the expression for the total derivative in the hint.

3. Jan 8, 2013

### physics2000

I kind of understand what you mean, but not sure what the first step is

4. Jan 8, 2013

### Dick

You've got dr in terms of the unit vectors with the hats on them. Write out grad(phi) in terms of the unit vectors and take the dot product.

5. Jan 9, 2013

### physics2000

is this what you mean?... i think I was overthinking it , thanks for your help!

[url=http://postimage.org/][PLAIN]http://s2.postimage.org/rgazdfeih/photo_7.jpg[/url] online photo storage[/PLAIN]

6. Jan 9, 2013

### Dick

Yes, I think that's what they want.