# Homework Help: Total differentials

1. Sep 6, 2008

### Riles246

total differentials!!

a.) f = 1/(x+y2)

b.) f = ln(x2y)

c.) P = [(RT)/(V-B)]-[A/(T1/2V2)]

what are the total differentials of these functions?

2. Sep 6, 2008

### cristo

Staff Emeritus
Re: total differentials!!

You need to show some work before we can help you. E.g. what is the definition of a total differential? What have you tried for each question?

3. Sep 6, 2008

### Riles246

Re: total differentials!!

so far these are the answers I have come up with...

A. [-1/((x+y2)2)]dx - [2y/((x+y2)2)]dy
I started this problem by moving the denominator up but i am not sure that was the correct first move.

b. (2xy/x2y)dx + (x2/x2y)dy

4. Sep 6, 2008

### cristo

Staff Emeritus
Re: total differentials!!

First two are correct. For the third, just do the same thing you've done in the first two, but this time the expression will have 5 terms.

5. Sep 6, 2008

### Riles246

Re: total differentials!!

for part C I assumed that A,B, and R are constants and the answer I came up with is..

[-RT(V-B)-2-AT-1/2*-2V-3)+(R/(V-B)+1/2AT-1.5V-2]

6. Sep 6, 2008

### Dick

Re: total differentials!!

Shouldn't there be a dT and a dV in there, as there were dx and dy in the other cases?

7. Sep 6, 2008

### Riles246

Re: total differentials!!

Woops. I forgot to put those in. Thanks!