What is the Error in Linking the Derivatives of the Traveling Wave Equation?

[Poetria]

Homework Statement

The traveling wave:
f(x,t) = sin(x-v*t)
It's the question about the relationship between $f_x$ and $f_t$

Relevant Equations

My reasoning was:

$$f_x=cos(x-v*t)$$
$$f_t=-v*cos(x-v*t)$$

so the relation between the two is:

$f_t=-v*f_x$

Why is this wrong?

My reasoning was:

$$f_x=cos(x-v*t)$$
$$f_t=-v*cos(x-v*t)$$

so the relation between the two is:

$f_t=-v*f_x$

Why is this wrong?

 

[pasmith]

Why do you think it's wrong?

 

[Poetria]

It's an automatic grader. :) I don't have a teacher.

 

[Delta2]

Maybe the question asks for the relationship between the second partial derivatives $f_{xx},f_{tt}$ cause those do appear in what we call the "wave-equation".

 

[Poetria]

Maybe the question asks for the relationship between the second partial derivatives $f_{xx},f_{tt}$ cause those do appear in what we call the "wave-equation".

You may be right, I will try. An excellent idea. :)

 

[vela]

What was the question exactly as it was worded?