a(n+1)+b(n+1)=1,b(n+1)=(1-an)/(1-an²)=1/(1+an),a(n+1)+1/(1+an)=1,a(n+1)an+a(n+1)+1=1+an,a(n+1)an+a(n+1)=an,1/a(n+1)-1/an=1,数列{1/an}为等差数列,公差为1,首项为4,1/an=4+n-1=n+3,an=1/(n+3),b(n+1)=1/...