U71=U1=U IB 20B △U。=U-U U-U 20B B I B U C tlk B 注意:zx=Z1+Z2=Z1+k2z2 K1 1 C k k U U I Z Z       − =   + 2 1 2 1 2 1 1 2 2 2 K K Z Z Z Z k Z Z Z Z Z Z k = + = +    = + = + 注意： 1 1 20 20 U U U U k k     − − = = U U U 1 1 1 = =   1 1 2 20 20 1 1 U U U U U U U k k       − −  = − = − = −  