1. The problem statement, all variables and given/known data Picked up Spivak's Calculus, 3rd ed. and just started. Got to this question and I'm honestly not sure how to start, I looked in the answer book which didn't really clue me in any more. If I understand the question it wants me to work within the four properties and show that there is no contradiction/they all have to apply? Not a native English speaker so I haven't had maths in English but that's what I got from it. More interested in how to approach it rather than answers, would assume there's coming a lot more similar questions. Not really done any proof based maths up until now.