If you FOILed out those factors, you would get a quadratic that is
[tex] x^2-qx-px-pq [/tex].
Combining "like" terms gives us
[tex] x^2-pqx-pq [/tex] when p and q are integers. That means that the constant, the last term in this quadratic, pq, is our constant, and that constant is the product of whatever p and q are.
