Please provide an explanation, I am confused

Evaluate or determine that the limit does not exist for each of the limits (a) lim f(x) x--4- (b) lim f(x) X--4+ and (c) lim f(x) x- -4 (Sided Limits: - 4" means when x approaches - 4 on the left side - 4* mean when x approaches - 4 on the right side) f(x) = x2 - 1, for x