Ok. So know that I am supposed to use one or more of the 12 basic properties of numbers from chapter 1 of Spivak's Calculus to prove this, but I can't see to figure out which one to start with. Can someone start me off here? Just a 'nudge.' edit: it says to 'prove' it, not to 'show' it. How do you 'prove' this? I can't see how to even start the proof.