$$u_{tt} = 4u_{xx} + \sin(t)x$$ $$u(3,t) = u(0,t) = 0$$ $$u(x,0) = \sin(\pi x/3)$$ $$u_t(x,0) = 3x^3 - 8x^2 $$ find the exact value of $u (1,1) $
My question for this problem is whether it is valid to use d'Alembert's Formula with $c = 2, x = 1, t = 1$ to get the numerical answer