For fraction equations (rational), only the denominator matters for the domain. Set it = to 0 and solve for x. That shows values not in the domain.
If the equation is
then x-15=0 and x=15 is not in the domain. The domain is all x where x is not = 15.
If the equation is (2/x) - 15 then the domain is all x where x not equal to 0.
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