1. The problem statement, all variables and given/known data Suppose that z=f(ax+by), where a and b are constants. Show that bz(x) = az(y). z(x) means partial derivative of z with respect to x, as for z(y). 2. Relevant equations 3. The attempt at a solution Say z=ax+by z(x) = a z(y) = b So bz(x) = ba = ab = az(y) I'm not sure that this is a correct analysis - because I know f(ax+by) doesn't necessarily mean z = ax+by... How should I interpret this problem?