R R 再求v 1 11 on R 12 vo 1 Ro R f R R R R V=1+1 on RRA (n+m4)-R1(m+n2) R R3 R RR 当R=R2=R=R=R,R=R时,R=R 于是 R 2再求 on v i 2 2 f i 1 1 f on v R R v R R v = − − ( ) ( ) 2 i 2 1 i 1 f 4 i 4 3 i 3 n p f o o p o n R v R v R R v R v R R R v v v = + − + = + 1 2 3 4 f p n 当R = R = R = R = R，R = R'时，R = R ( ) i 3 i 4 i 1 i 2 f o v v v v R R 于是 v = + − −