Science talk:Math Exam Resources/Courses/MATH220/April 2005/Question 11

This question is really strange, I wonder if the intention of it was to actually ask for the supremum of the set, which makes it much more interesting since it actually engages students with understanding what the supremum is. Here, the infimum of the set is really easy to find and really easy to find out of a misunderstanding of the question or the concept...

Yes, this is a little unclear.

This may be a little harsh, but I flagged the presented solution as GBS, for the following reasons: It should be cristal clear that an infimum has to satisfy two conditions, being less than any number of the set, and being the largest number with this property. This reasoning is somewhat there, but too convoluted in my opinion. Also, I would like to see some intuition applied here. And a clear plan of attack. Why y is not allowed to be positive is magic and only become clear later on. In fact, some more intuition rather than pure mathematical automatism applied here would make it easy to argue that we just have to check for candidates ${\sqrt {5}}<z<0$ in the first place.

I rewrote the proof completely using your feedback. We can still find the previous proof in the history of the page if needed. And as such, I'm flagging as RS again.

Well done, much clearer now. QGS.