1. The problem statement, all variables and given/known data Show ψ(x,t) = f(x-at) + g(x+at) satisfies the wave equation (a^2)*(∂^2ψ/∂x^2)-(∂^2ψ/∂x^2)=0 2. Relevant equations 3. The attempt at a solution I think i just take the derivative twice and end up with something like the second derivative = a^2*second derivative. However how do I actually take the derivative of an equation like this? I know it will involve the chain rule, but how exactly? Thanks for any help.