The domain of this function is all real numbers such that x does not equal 3.
We can tell this by looking at the equation for one of two things. The two things that typically disrupt a domain are dividing by zero and taking a square root of a negative. Since there are no square roots, we are only concerned with dividing by zero. So, we take the denominator and set it equal to 0.
x - 3 = 0
x = 3
This means that 3 is the value that makes the denominator 0 and therefor is the only x value we cannot use.
