The question is whether exam material should seem substantially different from the course material. Looking at your first question, I am hemming and hawing whe

The question is whether exam material should seem substantially different from the course material. Looking at your first question, I am hemming and hawing whether it is correct to say zero is positive or negative or both. I would say both, thus f''(x)=0 leads us towards a legitimate solution. Having not attended your course, it is possible the issue came up multiple times and this would cause no confusion. But it might confuse someone who has an otherwise excellent command of calculus. But given the homework problem shown later, it is rather likely that those paying attention found your exam question perfectly fair. "Was this exam question harder than my homework problem sets? Absolutely not! It's just different." The kind of differences matter. I do not see why the exam questions need to seem different in any non-trivial way. (I speak of a general principle. I do not hold an opinion about your particular questions.)