# Thread: Not understanding these functions inside of functions...

1. ## Not understanding these functions inside of functions...

Can somebody explain this to me?

Find:

$\frac{\partial^2g}{\partial t^2}$

where $g(r,s)$ is an arbitrary function and

$r(x,t)=x+ct$ and $s(x,t)=x-ct$

2. Originally Posted by billym
Can somebody explain this to me?

Find:

$\frac{\partial^2g}{\partial t^2}$

where $g(r,s)$ is an arbitrary function and

$r(x,t)=x+ct$ and $s(x,t)=x-ct$

Since you indicate that you are having trouble with these kinds of derivatives in general, I think it would be best to just link you to this:

http://tutorial.math.lamar.edu/Class...ChainRule.aspx

Your example is a very basic one, so see if you can find the derivative after reading the tutorial.

3. thanks! just what I needed.