n=1时,bn=2-2S1=2-2b13b1=2b1=2/3n≥2时,Sn=(2-bn)/2=1- (1/2)bnbn=Sn-S(n-1)=1-(1/2)bn-1+(1/2)b(n-1)(3/2)bn=(1/2)b(n-1)bn/b(n-1)=1/3,为定值数列{bn}是以2/3为首项,1/3为公比的等比数列bn=(2/3)(1/3)^(n-1)=2/3&...