T cp(x)sin ndx op(-t)sin(-nt)d(t) 几冗 x)sin nxar C v(x)sin ndx=B(n=1, 2,. n 5 βn − bn = (x)sinnxdx 1 − − − − = ( )sin( ) ( ) 1 t nt d t − − = − ( x)sinnxdx 1 − = − (x)sinnxdx 1 = −n (n = 1,2, ) , an = n . bn = −n