U(Y)≈U(Y-元Z)+ZU/(Y-元Z)+ 元2z2U(Y-元2 U(Y-2=U(Y-元z)-(1-元)ZU(Y-元+ (1-元)2zU(Y-元2) In which case, the equation becomes 0=(亓-7)ZU(Y-元2+(+(1-元)2)2 or (元-)=200元2(1-2元+2元UY  UY   Z   ZU Y   Z  1 2   2 Z2UY   Z UY  Z  UY   Z  1   ZU Y   Z  1 2 1   2Z2UY   Z In which case, the equation becomes: 0      ZU Y   Z  1 2    2  1   2Z2U or       U Y Z 2U Y Z 1  2    2   2 