(3)以B为坐标原点，写出波动方程 y4=0.03cos4πt → 1.8m.+5m+.9m.d C OB A D 26 △0=pg-04= 三元 PB=元 yB=0.03cos(4πt+π) y=003s25+ =π  B =π 0.03cos(4π π) B y t = + 0.03cos[2π( ) π] 0.5 10 t x y = − + u C B A D 5m 9m o x 8m y t A = 0.03cos 4π （3）以 B 为坐标原点，写出波动方程 2 B A        = − =