Well your function is

For a function to be continuous at a point, the function needs to approach the same value from the left as it does from the right.

To the left of , the function is equal to , and so will approach as from the left.

To the right of , the function is equal to , and so will approach as from the right.

Since the function at does not approach the same value from the left as it does from the right, the function is discontinuous at .