# Help with Laplace eqution

1. Jun 19, 2015

### avi89

its the question in the middle

2. Jun 19, 2015

### axmls

Do you know the general formula for the Laplace transform of the nth derivative?

3. Jun 19, 2015

### SteamKing

Staff Emeritus
If you look at a table of Laplace transforms, like the one attached to this article:

https://en.wikipedia.org/?title=Laplace_transform

You'll see a formula for finding the first or second derivative, f' and f", for example. Look below to the entry for "general differentiation" and f(n), and you'll see a formula for LT for finding higher-order derivatives.

In your case, n = 4, but you appear to be missing some initial conditions necessary to apply the formula, namely y"(0) and y'''(0).

4. Jun 19, 2015

### avi89

this is what i was thinking! some initial conditions are missing to use the derivative forumula, so maybe there's another way to solve.
also, notice that this is not the 4th derivative of y, but power(y,4) .. it got me confused

5. Jun 19, 2015

### Strum

Why would you use the laplace transform to solve equations involving $y^4$ ? You will just get a lot of convolution integrals.

6. Jun 19, 2015

### pasmith

Are you sure it isn't a badly-written $y''$? That would make it a question of solving a linear 2nd-order ODE subject to the two given initial conditions.

7. Jun 20, 2015

### avi89

aww god, i think you're right!
sighh

8. Jun 21, 2015

### Carlos Gouveia

There's a difference between the 4th derivative of y (y'''') and y⁴. Since this latter is a non-linear term and being the Laplace a linear operator, I'm afraid an ODE involving y⁴ has no solution by the Laplace method. It seems to me that your problem has a typographical error.