# Math Help - Chain Rule for 2 Variables

1. ## Chain Rule for 2 Variables

Let a=x-ct and b=x+ct. Show that fab=ftt-c2fxx. Hint: The chain rule for 2 varibles is daf(x,y)=fxxa+fyya.

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