Thread: Chain Rule for 2 Variables

Let a=x-ct and b=x+ct. Show that f_ab=f_tt-c²f_xx. Hint: The chain rule for 2 varibles is d_af(x,y)=f_xx_a+f_yy_a.

I'm assuming that f(a,b), a(x,t), and b(x,t).

Thanks in advance.

Hey karebear688.

Show us what you have tried.