b=(a-1)/(a+1)=(a+1-2)/(a+1)=1-2/(a+1)即 a=[2/(1-b)]-1=(1+b)/(1-b)
b=(a-1)/(a+1)=(a+1-2)/(a+1)=1-(2/a+2)2/a+2=1-ba+2=2/(1-b)a=2-2/(1-b)
b(a+1)=a-1ab+b=a-1a(1-b)=(1+b)a=(1+b)/(1-b)