1. The problem statement, all variables and given/known data Prove that the electromagnetic wave equation: (d^2ψ)/(dx^2) + (d^2ψ)/dy^2) + (d^2ψ)/(dz^2) − (1/c^2) * [(d^2ψ)/(dt^2)]= 0 is NOT invariant under Galilean transformation. (i.e., the equation does NOT have the same form for a moving observer moving at speed of, say, v in the x direction). *note: all the "d"s in this equation are the partial derivatives. 2. Relevant equations galilean transformation: t'=t, x'=x-vt, y'=y, z'=z 3. The attempt at a solution -from what i understand to solve this involves the chain rule for partial derivatives. -looking at the equation i cant help but jump to something with the gradient of ∇ψ, but i dont know where to go from there.