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