The given domain is . This specifies what values of x are legal, not what values of 2x are legal. So if x can be any value in the interval , then 2x can be anywhere in the interval .
For lack of a better name...
Anyway, here's my problem. In the answers (second image uploaded), they've stated that it's okay to use values outside the domain, as long as they'll eventually fit in the domain as values of x. Is this okay?
This would be meaningless without the images...so take a look at them