Au B, Iba,R Ba2RL BRi bel 而 A 2=B1a2≈B b1 61 21 2 1 2 2 1 1 1 2 1 1 1 1 2 1 1 1 1 2      =  =  =     −  = −  = = − a I I I I I I I I A r R r a R r I I a R U U A e c b c b c i o i b e L b e L b e b b L i o u 而