**·**2011-08-06 06:52:23

I find it intriguing that u ask a qn and dont follow up for three days!

Anyway, the solution:

Letting x = -1991, we get (1991-b)(1991-c) =1, so that either b = c = 1990 or, b = c = 1992

Again setting x=-a, we get (a-b)^{2}=1 so that a-b=Â±1

Noting that a â‰ 1991, we get a=1989 or 1993