r dB 1=b·t6.E COS 2r dt 2 ∫E·d=- E,cos·d(b·t26) 45 R dB cosb·d(btn) 0 26/cos dt R dB c450 4 cos0sec 0d0 2 dt R2丌dB 8 dt2 , , , cos 2 g r b R dB r l b t E r dt   = =  = 0 0 0 0 0 0 0 45 2 0 2 45 0 2 45 45 2 2 0 0 2 cos ( ) cos ( ) 2 / cos cos sec 2 8 r g g E dl E d b t R dB d b t b dt R dB d dt R dB dt           = • =    =    = =    