The limit as x approaches 3 from the left side is 1 due to the fact that the graph shows the function approaching 1 as the graph moves toward 3. The main way to tell a limit is not what the function is at the value, but what it is next to the value. The negative after the 3 says that the limit is a left sided limit, meaning it wants to know what the value approaches from the left handed or 'negative' side.
