I have the equation -(ck^2)U(k,t)=d^2/dt U(k,t). And I need to find the general solution.
The Attempt at a Solution
I can rearrange this into the form d^2 U/dt^2 + (ck^2)U(k,t)=0 but I am not sure of the form of the solution to this equation.
could someone please give me pointer in the right direction