Answer :
that's the numbers you can use for the input
exapmle, for f(x)=1/x, we aren't allowed to use 0 for the domain because we would divide by 0, so our domain is all real number except 0
exapmle, for f(x)=1/x, we aren't allowed to use 0 for the domain because we would divide by 0, so our domain is all real number except 0