Let us take some examples.

1. Find domain of the function f(x) = 1/(x - 5)

Solu: Given, f(x) = 1/(x - 5)

Now, this function is not defind when x - 5 = 0 i.e. x = 5 because it will give the value 1/0 which is not defined.

So, Dom(f) = R - {5}

2. Find domain of the function f(x) = (2 + x)/(2 - x)

Solu: Given, f(x) = (2 + x)/(2 - x)

Now, this function is not defind when 2 - x = 0 i.e. x = 2 because it will give the value 4/0 which is not defined.

So, Dom(f) = R - {2}

In this way, we find the domain of a function when a function in form of division is given.

Hope you got the point.