Explanation:
you mean "which value is not part of the domain", right ?
f(x) = 1/(x - 4)
the domain of a function is the interval or set of all valid values for x.
invalid values for x are values for which the function did not have a defined y-value (= functional result).
so, for what value of x does this function not have a defined result ?
well, it is essentially a fraction. and fractions are all good and fine until we suddenly have one in the form of x/0, which means a division by 0.
that is undefined.
when is our function fraction suddenly dividing by 0 ?
when x - 4 = 0
x - 4 = 0
x = 4
so, x = 4 is not part of the domain of this function.