3A3 R-(R-R coS 0)2d8 jt- sinead.(注意n=siD 2R3子 (1-sin0)de 3 R 3 − = − − 2 2 2 3 3 2 2 2 [ ( cos ) ] 3 1   R R R  d     d R [1 sin ] 3 2 2 3 3  − = −  = − 2 0 3 3 (1 sin ) 3 2   d R ) 3 4 ( 3 3 =  − R ( (sin ) |sin |) 2 3 3 2 注意  = 