(chain rule)
Question
Suppose z=f(x-ct) + g(x+ct), where c is a constant. Show that
z(tt)=c^(2)z(xx)
Where z(tt) means the second partial derivative of z with respect to t, as for z(xx) as well.
I know this involves some application of the chainn rule but I can't seem to prove it at all... please help!