a5=c1(5) 0l=C1(5)+f2(n) 即(2,n)=f(2)+(m)<4> 故通解为 u(x,y)=f(x+ at)+f2(x-atò = + ¶ ¶ = ¶ ¶ ( ) ( ) ( ) 1 x 1 x 2 h x x x d C f u C u 即 u(x ,h) = f 1 (x ) + f 2 (h) < 4 > 故通解为： ( , ) ( ) ( ) u x y = f 1 x + at + f 2 x - at