bn O「 O Esinot sinnott T EOrol cos(n-Dot-cos(n+1)otdr 2丌0 b1=o Esinot sin tdt EOrt Eol sin 2ot E (1-c0s20t)dt= 210 2丌 20 2 0 n>1时 Eol sin(n-1)ot sin(n+1)ot 2T(n-1)o(n+1)ob Esin t sin t d t π π 0 1         n t n t t E cos( 1) cos( 1) d 2π π 0                   ( 1) sin( 1) 2π n E n t bn 0 ( 1) sin( 1) 0 π           n n t b E t n t t n sin sin d π π 0        t t E (1 cos2 )d 2π 0        0 π 2 sin 2 2π             t t E 2 E  n > 1 时