# A tricky ODE

1. Nov 6, 2009

### Daniel D

Hi,

I came across the following differential equation:

$$\sqrt{1+(y')^2}=\frac{d}{dx}\left(y\frac{y'}{\sqrt{1+(y')^2}}\right)$$

I found possible solutions: $$y\left(x\right)=cosh(x+C_{1})$$.
However, this is a second order ODE so there exist a more general solution, with 2 freedom degrees.

Can anyone find it?

Thank you.

2. Nov 6, 2009

### Staff: Mentor

What do you mean "can anyone find it"? Please show us how you have tried to find it so far. This is the PF, not Yahoo answers.