Okay, I feel really dumb, because this seems like something I should know, but I don't. So, here's my question. Suppose I have d2y/dx2, x = x(z), and z = z(x) How do I find d2y/dz2? Here's what I did: dy/dz = dy/dx * dx/dz d2y/dz2 = d/dz ( dy/ dz ) = d/dz (dy/dx * dx/dz) = d2y/dx2 * (dx/dz)^2 + dy/dx * d2x/dz2 Is that OK? Is there an easier way to do this?