# Homework Help: Solving x=ytan(y)

1. Jan 27, 2012

### H_man

I am trying to solve x=ytan(y)

x is an independent function of which I know the value. I wish to solve for y.

I can do this numerically. But I was really hoping someone out there had seen an analytical technique.

Anyone???

2. Jan 27, 2012

### tiny-tim

Hi H_man!
Sorry, numerically is the only way.

(But why do you want to solve it at all? It presumably isn't from trigonometry. )

3. Jan 27, 2012

### H_man

It's to match the boundary conditions of a corrugated waveguide.

I guess I'll just have to do it the messy way :-(

Thanks tiny-tim

4. Jan 27, 2012

### Xyius

You can always approximate tan(y) by a couple of terms in its Taylor Expansion ;]

5. Jan 27, 2012

### vela

Staff Emeritus
Do you need the actual solutions or just need to get an idea of how they behave? If it's the latter, you can analyze the equation graphically.

6. Jan 27, 2012

well, maybe you could expand the Taylor series for ytan(y) and then find the inverse of this function using Lagrange inversion theorem and see if the series obtained for the inverse function has a positive radius of convergence? That's one way.

7. Jan 28, 2012

### H_man

Hi Vela, I'm looking for exact solutions, I've already produced pretty graphical plots to get the general idea.

Hi AdrianZ, before your post I'd never heard of the Lagrange inversion theorem. I will try this method and let you know if it succeeds.

Thank you both for your suggestions.