则在r'<z-b<R内 R f() f() 2丌i 1 ∑ (-b b5-z5-b-(2-b)k -b)则在 r ¢ < z - b < R ¢内 ( ) ( ) ( ) ( ) ( ) ú û ù ê ë é - - - = ò ò 2 1 2 1 l l d z f d z f i f z x x x x x x p ( ) ( ) ( ) å ¥ = + - - = - - - = - < - - 0 1 1 1 1 : 1, k k k b z b b z b z b z b l x x x x b r r¢ R 2 l 1 l