# Differential equation

1. Aug 31, 2010

### shseo0315

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

(1+x)^2 dy/dx = (1+y)^2

2. Relevant equations

3. The attempt at a solution

The post I put up a while ago actually turns out to be the one above.

So far I'm not getting the right answer, please help.

2. Aug 31, 2010

### epenguin

You can get everything involving x on one side, everything involving y on the other. Called 'variables separable'. Look up.

Edit - just as was your previous one I have now seen which you did manage to do!

3. Aug 31, 2010

### shseo0315

Thanks.
But on the way, 1/(1+x^2)dx = 1/(1+y^2)dy
if I take an intergral, I get

-1/(x+1) + c = -1/(y+1) + c

This is 1/(x+1) + c = 1/(y+1) right?

The answer states that y = (1+x)/[1+c(1+x)] -1

I don't know how to get there.

4. Aug 31, 2010

### Dick

Right. You never really needed two c's. Just take your expression and use algebra to solve for y.

5. Aug 31, 2010

### mmmboh

Inverse both sides to find y+1, and then just subtract one from both sides to solve for y.

6. Aug 31, 2010

### shseo0315

from 1/(x+1) +c = 1/(y+1)

that is y+1+c = x+1 right

y(x) = x+c

this is what I get, but the answer is quite different

which is y = (1+x)/[1+c(1+x)] -1

7. Aug 31, 2010

### Dick

1 over 1/(x+1)+c isn't equal to (x+1)+c. Use correct algebra. Not just any algebra.

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