Let be bounded above, then is bounded above and
Okay, I think there's no much to do here, we have and so is bounded above and besides Is it correct?
Now if is bounded below, then
Well since so and we're done. Is it correct?
Think about the following
(releasing the variable of might greater values)
.................................. (as the variables of and are un related, we can split it)
.................................. . ( does not depend on the letter of the variable)
Probably, this will help you understand it easier.
You can do the same for .