# Chain rule

1. Feb 10, 2014

### mrmojorizing

Hi fi you look at quesiotn 16b in the following link they try to find dE/dx.

they use the chain rule. the chain rule says dF/dt=dx/dt*dF/dx+dy/dt*dF/dy if F=f(x,y) and x=f(t) and y=f(t).

But in 16b they're trying to find dE/dx and as part of the use of the chain rule they try to find dt'/dx (in the first equation under where it says 'a galilean transform...') however t' is not a function of x, so i don't understand why they're taking the derivative of t' wrt to x.

http://stuff.mit.edu/afs/athena/course/8/8.20/www/sols/sol1.pdf

2. Feb 10, 2014

### vanhees71

That's very simple,
$$\frac{\partial t'}{\partial x}=0.$$