解方程r"()+(m)3()=0(n≠1)必须知道Tn的初始条件 带入初始条件x0=∑(0os=0()=29 n7 u4(x,1)=∑T() v(x)=∑vn,cos 7(O)=9=7o(5kl5 7o'(0)=vo=15 ∥(d5 T2(0)=q J(5)c0+n5 d T"(0)=vn=1 y()cos nrts 得解 70()=+v0t n刀t 1(O)=%0s=n inin带入初始条件    =  = = = = 0 0 ( ,0) (0) cos ( ) cos n n n n l n x x l n x u x T        =  = = = = 0 0 ( , ) '( ) cos ( ) cos n n n t n l n x x l n x u x t T t        d l T l  = = 0 0 0 ( ) 1 (0) ''( ) ( ) ( ) 0 ( 1) 2 + T t = n  l n a T t n n 解方程  必须知道 Tn 的初始条件    d l T l  = = 0 0 0 ( ) 1 '(0)       d l n l T l n n ( )cos 2 (0) 0  = =       d l n l T l n n ( )cos 1 '(0) 0  = = 得解 T t t 0 0 0 ( ) = + l n at n a l l n at T t n n n     ( ) = cos + sin