(3) Z,=(1+δ)Z,Z3=(1+δ)Z,Z2=Z4=Z -26-82 -δ uo (2+y4,≈24，（3） 132 4 2 2 (1 ) , (1 ) , 2 (2 ) 2 O SS Z ZZ ZZ Z Z u uu δ δ δδ δ δ = + =+ = = −− − = ≈ +