s a= Sou(t)cos tdt =S E sint cos tdt=0 T T 4E11 ut= cos2tc0s4、 cos ot. 兀23 15 35 2E 11-2∑ cos 2nX H=1 4n2-1 (-00<x<+) 上页  =  1 0 ( )cos 2 a u t tdt   =  0 sin cos 2 E t tdt = 0, cos6 ) 35 1 cos4 15 1 cos 2 3 1 2 1 ( 4 ( ) − − − −  = t t t E u t (−  x  +) ]. 4 1 cos2 [1 2 2 1  2  = − −  = n n E nx