(5) (10 points) What is the solution to the wave equation \[ \frac{\partial^{2} u}{\partial t^{2}}=4 \frac{\partial^{2} u}{\partial x^{2}} \] on the interval \[ 0 \leq x \leq \pi \] with the boundary conditions \[ u(0,t)=0 \] and \[ u(\pi ,t)=0 \]?