If our function is

then is defined exactly where is defined and non-negative; that is, where

By two reversible operations, we find that this is equivalent to saying

Therefore, must be positive and must lie in the first or third quadrant. Now, if we knew that were positive, we could divide by to obtain

but in the third quadrant, , and we can't do this without reversing the inequality. In fact, while your answer is correct in the first quadrant, in the third quadrant it will be

Hope this helps!