# Homework Help: Cant get to grips with re arranging formulae

1. Nov 2, 2008

### chaz699

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

basically i can't get to grips with rearranging formulae

the question is

make U the subject

fv = uv
u+v

(uv is divded by u+v)

2. The attempt at a solution

i try at making them into brackets etc but i can't get to it

can someone show me step by step how to do it

thanks, much appreciated

2. Nov 2, 2008

### Hootenanny

Staff Emeritus
Welcome to Physics Forums.

We won't show you how to do the question, but we will help you do it yourself.

When trying to make something the subject of a formula the best thing to do is to get it out of the fraction. How could you get (u+v) out of the fraction?

3. Nov 2, 2008

### chaz699

erm, put it on the other side of the formula?

4. Nov 2, 2008

### Hootenanny

Staff Emeritus
Sounds good. So what does that give you?

5. Nov 2, 2008

fv(u+v)=uv ?

6. Nov 2, 2008

### Hootenanny

Staff Emeritus
Looks good. What do you think the next step would be?

7. Nov 2, 2008

### chaz699

erm multiply out the brackets?

8. Nov 2, 2008

### Hootenanny

Staff Emeritus
Sounds good.

9. Nov 2, 2008

### chaz699

so would it be

fu+fv+vu+v(squared)=uv

10. Nov 2, 2008

### Hootenanny

Staff Emeritus
Not quite, note that to expand the bracket you would just multiply everything in the bracket by fv. Do you follow?

11. Nov 2, 2008

### chaz699

i dont quite understand that bit

12. Nov 2, 2008

### Hootenanny

Staff Emeritus
Okay what is 2(3+4)?

13. Nov 2, 2008

### chaz699

answer is 14

14. Nov 2, 2008

### Hootenanny

Staff Emeritus
Correct, which is the same as 2x3 + 2x4. Does it make sense now?

15. Nov 2, 2008

### chaz699

er no hah

i dont see how my answer is wrong

16. Nov 2, 2008

### chaz699

would it be FVU+FV(squared) = UV

17. Nov 2, 2008

### Hootenanny

Staff Emeritus
Much better .

What do you suppose the next step is?

18. Nov 2, 2008

### chaz699

i actually have no idea

19. Nov 2, 2008

### Hootenanny

Staff Emeritus
Try moving all the terms with u in onto the same side.

20. Nov 2, 2008

### chaz699

so then it would be

fv(squared) = uv-fvu?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook