MHB Partial Differential Equation: Is There an Easy Way to Solve This?

Click For Summary
The discussion centers on solving a specific partial differential equation involving variables u, v, and A. The original poster seeks a method to simplify the equation by merging differentials on the right side. They present their calculations, which lead to a reformulation of the equation. Another participant points out a mistake in the calculations related to the differential of one term. The conversation highlights the complexities of manipulating partial differential equations and the importance of accuracy in the derivation process.
Telemachus
Messages
820
Reaction score
30
I have this partial differential equation that I have to solve, and I thought that perhaps there was an easy way of solving this, like finding an equivalent differential for the right hand side of the equation, on such a way that I could get a simple differential equation, and then just integrating I could solve this.

The partial differential equation that I have to solve is this:
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})$$
Is there an easy way for solving this? the idea I had was to merge both differentials on the right side in only one differential, but I couldn't find the way.

I'm sorry, I wanted to post this in differential equations, I made a mistake posting this here.

---------- Post added at 08:36 PM ---------- Previous post was at 06:52 PM ----------

Ok. I think I got it. This is what I have done:
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})$$

So I took
$$d(A^{-1/2}u^{-3/4}v^{1/2})=A^{-1/2}(-\frac{3}{4}u^{-7/4}v^{1/2}du+\frac{1}{2}u^{-3/4}v^{-1/2}dv)$$
And in the other hand:
$$d(2A^{-1/2}u^{1/4}v^{-1/2})=A^{-1/2}(\frac{1}{2}u^{-7/4}v^{1/2}du+u^{1/4}v^{-3/2}dv)$$

Then
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})=A^{-1/2}(-\frac{3}{4}u^{-7/4}v^{1/2}du+\frac{1}{2}u^{-3/4}v^{-1/2}dv+\frac{1}{2}u^{-7/4}v^{1/2}du+u^{1/4}v^{-3/2}dv)$$
$$d \left( \frac{\mu}{T} \right )=A^{-1/2}[ -\frac{1}{4}u^{-3/4}v^{1/2}du-\frac{1}{2}u^{1/4}v^{-1/2}dv]=-\frac{1}{4}[u^{-3/4}v^{1/2}du+2u^{1/4}v^{-1/2}dv]=-A^{-1/2}d(u^{1/4}v^{1/2})$$

PD: Thanks for moving it :)
 
Last edited:
Physics news on Phys.org
Ulysses said:
I have this partial differential equation that I have to solve, and I thought that perhaps there was an easy way of solving this, like finding an equivalent differential for the right hand side of the equation, on such a way that I could get a simple differential equation, and then just integrating I could solve this.

The partial differential equation that I have to solve is this:
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})$$
Is there an easy way for solving this? the idea I had was to merge both differentials on the right side in only one differential, but I couldn't find the way.

I'm sorry, I wanted to post this in differential equations, I made a mistake posting this here.

---------- Post added at 08:36 PM ---------- Previous post was at 06:52 PM ----------

Ok. I think I got it. This is what I have done:
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})$$

So I took
$$d(A^{-1/2}u^{-3/4}v^{1/2})=A^{-1/2}(-\frac{3}{4}u^{-7/4}v^{1/2}du+\frac{1}{2}u^{-3/4}v^{-1/2}dv)$$
And in the other hand:
$$d(2A^{-1/2}u^{1/4}v^{-1/2})=A^{-1/2}(\frac{1}{2}u^{-7/4}v^{1/2}du+u^{1/4}v^{-3/2}dv)$$

Then
$$d \left( \frac{\mu}{T} \right )=ud(A^{-1/2}u^{-3/4}v^{1/2})+vd(2A^{-1/2}v^{-1/2}u^{1/4})=A^{-1/2}(-\frac{3}{4}u^{-7/4}v^{1/2}du+\frac{1}{2}u^{-3/4}v^{-1/2}dv+\frac{1}{2}u^{-7/4}v^{1/2}du+u^{1/4}v^{-3/2}dv)$$
$$d \left( \frac{\mu}{T} \right )=A^{-1/2}[ -\frac{1}{4}u^{-3/4}v^{1/2}du-\frac{1}{2}u^{1/4}v^{-1/2}dv]=-\frac{1}{4}[u^{-3/4}v^{1/2}du+2u^{1/4}v^{-1/2}dv]=-A^{-1/2}d(u^{1/4}v^{1/2})$$

PD: Thanks for moving it :)

Hi Ulysses, :)

I think you have a mistake in the third line. It should be,

\[d(2A^{-1/2}u^{1/4}v^{-1/2})=A^{-1/2}\left(\frac{1}{2}u^{-3/4}v^{-1/2}du-u^{1/4}v^{-3/2}dv\right)\]

Kind Regards,
Sudharaka.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 3 ·
Replies
3
Views
998
  • · Replies 2 ·
Replies
2
Views
820
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K