Quadratics and parabola

For each positive integer $n$ , the parabola $y=(n^{2}+n)x^{2}-(2n+1)x+1$ cuts the x axis at the points $A_{n}$ and $B_{n}$ .What is the value of $\displaystyle \sum_{n=1}^{1992}A_{n}B_{n}$

This problem is a part of my set Some JEE problems