lim x→2 means what is the value of y as x approaches 2 from the left side and the right side - they must be the same value for the limit to exist. "Approaches" is the operative word - it does not have to exist at that y-value, as in example a. (Use it in a sentence: if you are approaching someone, then you are walking towards them and getting close but do not become that person.)
* lim x→1 [g(x)] = DNE because (left side of 1) lim x→1- [g(x)] = 2 and (right side of 1) lim x→1+ [g(x)] = 1
(a) lim x→2 [f(x) + g(x)] = 2 + 0 = 2

3+f(x)