x t y(x, t)=ACOS 2T(---)=Acos 2丌 x-ut T 2丌 y(x,t)=Acos(r-ut) t x y(x, t)=Acos 2r )=AcoS(@ t-h) T n y(x,t)=Acos(@ t-kx)k 2丌 角波数角波数 ( , ) cos 2 ( ) x t y x t A T   = − 2 A x ut cos ( )   = − 2 y x t A x ut ( , ) cos ( )   = − ( , ) cos 2 ( ) cos( ) t x y x t A A t kx T    = − = − y x t A t kx ( , ) cos( ) = −  2 k   =