The number of integral values of a for which the quadratic equation (x+a)(x+1991)+1 = 0 has integral roots are
3
0
1
2
(x+a)(x+1991)+1 = 0
⇒ (x+a)(x+1991) = -1
⇒ (x+a) = 1 and x+1991 = -1
⇒a = 1993 or x+a = -1 and x+1991 = 1
⇒ a= 1993 or a = 1989