Only possible values we need to exclude are values that would give us 'number' with zero in denominator. So set x²-9 (assume x²-9 is denominator) equal to 0. X² — 9=0From here, solve for x; x²=9 x=±√9 x=±3So we cannot have -3 and 3 being in our domain. So restrictions of domain is x ≠ -3 and x ≠ 3.