Question

Step by step please. (>人<)

Answer 1

recall that when a fraction has a denominator of 0, the fractions becomes undefined

so any restrictions to a rational, or fraction, will be in making sure that it doesn't become undefined

so give "y" values that doesn't make that happen

Answer 2

and the restrictions will be values "y" must be restricted by
that is, values "y" must not take since that'd make the denominator 0

Answer 3

-1

Answer 4

(・_・ヾ