Explanation:
A hole in the graph is a point in the graph that does not exist because of a restriction in the domain.
Here is an example.
Think of the equation y = x + 5.
The graph of this equation is a straight line with slope 1 and y-intercept 5.
There is no restriction on the domain. The domain is the entire set of real numbers, and the range is also the entire set of real numbers. Every point on the line is part of this equation. There are no "holes".
Now take that equation, and modify it by multiplying both the numerator and denominator by x + 2.
You now have the equation:

You could have this equation given to you as
,
but if you simplify it, you will get back to
.
Now look carefully at the equation in the form
.
You know that you can divide the numerator and denominator by the common factor x + 2, leaving the equation simplified as
y = x + 5, but there is one thing you must add to the simplified equation: it is the restriction.
y = x + 5; x ≠ -2
The graph of

is a straight line, just like the graph of y = x + 5, but because of the binomial x + 2 in the denominator, it has the restriction on the domain of x ≠ 2, which in fact is a hole at x = -2.
The way you find holes is by looking at restrictions on the domain. Typically, you set the denominator equal to zero, and solve for x. Any value of x that causes the denominator to equal zero must be excluded from the domain causing a hole.