- #1

- 39

- 0

## Homework Statement

http://imgur.com/gTapO

## Homework Equations

## The Attempt at a Solution

The first one is easy, just use the fact that δ

_{i}= δ/δx

_{i}and it reduces to the sum from with i=1,2,3 of δx

_{i}/δx

_{i}= 1 + 1 + 1

I tried to do a similar thing with the second one, also using the fact that r = |x| = √(x dot x), but for some reason I can't make any progress. Since r is a scalar, can't I pull it out of the original dot product and have the following:

1/r * (∇ dot u)

Well, obviously I can't because that would give me 3/r rather than 2/r.

I've made no progress on the third one so far, so any advice is appreciated.

Thanks!