1. The problem statement, all variables and given/known data The problem is: Show that an [itex]\rightarrow[/itex] [itex]\infty[/itex] iff for all [itex]\Delta[/itex] > 0, [itex]\exists[/itex]N such that n [itex]\geq[/itex] N [itex]\Rightarrow[/itex] an [itex]\rightarrow[/itex] [itex]\infty[/itex] 2. Relevant equations Not sure if there are any 3. The attempt at a solution I can't really think of anything to do here because I have absolutely no clue what [itex]\Delta[/itex] is meant to be- my only guess was the difference between the sequences an and aN... and I can't conceptualize this either. EDIT: I did some google searching, and I understand what this definition means but I have no idea how to approach it. One idea I have is that it is similar to the definition of a limit- I could possibly use something along the lines of a general limit proof to prove this statement.