an=3+2(n-1)=2n+1lim[1/(a1a2)+1/(a2a3)+...+1/(a(n-1)an)]=lim(1/2)[1/3-1/5+1/5-/7+...+1/(2n-1)-1/(2n+1)]=lim(1/2)[1/3-1/(2n+1)]n->∞,1/(2n+1)->0lim[1/(a1a2)+1/(a2a3)+...+1/(a(n-1)an)]=1/6