xx+ Tu x=(pdx )u T x x+dx xx dx Turr-pu=0 波动方程。u1-a2lx=0 2 TIp a at a 1 a 0 x= at ax ax at a at a波速T ux x dx Tux x dx utt ( ) 2 + − 1 =  t t x x d x x x u dx u u T =  + − Tuxx − utt = 0 /  2 a = T 0 2 波动方程。 utt − a uxx = 波速 x at = t 1 x x t a t     = =     0 1 2 2 t t − ut t = a u a a