关键和难点是求出 3s g(o)s(o)∑bF (2T)yo vga, q) (3-48)◼ ∴关键和难点是求出 ( ) ( ) ( ) ( )    = =  s i q i s i i q V dS g g 3 1 3 3 1 2      ＝  ＝ (3-48)