There are three real numbers that are not in the domain of

f(x) = (x - 1)(x - 2)(x - 3)/(x(x - 1)(x - 2))

What is the sum of those three numbers?

[(x - 1)(x - 2) (x - 3)] / [ x ( x -1) ( x -2) ]

Any x that makes the denominator = 0 is not in the domain

So x = 0 x = 1 and x = 2 are not in the domain

(We will have "holes" at x = 1 and x = 2 and a vertical asymptote at x = 0 )