1.
a(n+1)+1=an^2-n*an+1+1=an^2-n*an+2>2(an+1)
a(1)>=3
1/(1+a(1))……
>1-1/3-1/3^2-……-1/3^n
=1-(1/3)*(1-1/3^n)/(1-1/3)
>1-(1/3)*1/(1-1/3)
=1/2
故(3/(3-1))*(3^2/(3^2-1))*……*(3^n/(3^n-1))
1.
a(n+1)+1=an^2-n*an+1+1=an^2-n*an+2>2(an+1)
a(1)>=3
1/(1+a(1))……
>1-1/3-1/3^2-……-1/3^n
=1-(1/3)*(1-1/3^n)/(1-1/3)
>1-(1/3)*1/(1-1/3)
=1/2
故(3/(3-1))*(3^2/(3^2-1))*……*(3^n/(3^n-1))