# Differential equation

1. Jul 8, 2010

### thereddevils

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

Find the general equation of differential equation dy/dx=y+x

2. Relevant equations

3. The attempt at a solution

I don see a way to separate the variables. What substitution should i use?

2. Jul 8, 2010

### Office_Shredder

Staff Emeritus
I only see three possible choices for a function in your equation: x, y, or x+y

3. Jul 8, 2010

### thereddevils

sorry but i don get what u meant

4. Jul 8, 2010

### Dick

I think Office_Shredder means you should look at the equation and take a guess at what might be a good substitution. What might work?

5. Jul 8, 2010

### hunt_mat

Failing that, you could try an integrating factor of e^{-x}

6. Jul 8, 2010

### HallsofIvy

You said you were looking for a substitution! It wouldn't do much good to let u= x or u= y, would it? So what if u= x+ y?

7. Jul 8, 2010

### LCKurtz

Substitution?? Have you studied linear equations or constant coefficient equations yet?