It will certainly be impossible to do this without knowing the definition of "continuous at x= a"! And that is that . You will also need to know that the limit exists only if the limits, from above and below, both exist and are equal.
So for the first problem, to determine whether or not if , if x> 1, You need to show that
and are the same and equal to f(1).
(For the last one you need to think about .
What do you remember about ?