$(x,t)={\displaystyle \underset{0}{\overset{x-ct}{}}}h()d+(x+ct).\frac{?}{\text{t}\text{h}\text{e}\text{f}\text{i}\text{n}\text{a}\text{l}\text{f}\text{u}\text{r}\text{m}d}$

Oerive

Wave equarlin