If y = a sin `(2pi) / (lambda) (vt - x),` then
`(d^2y) / (dt^2) = v^2 (d^2y) / (dx^2)`
`(dy) / (dx) = v2 (dy) / (dt)`
`(d^2y) / (dx^2) = v^2 (dy) / (dx)`
`(dy) / (dt) = v^2 (dy) / (dt)`
how to solve?