x=(10690−4990) (xn−an) is divisible by both (x - a) and (x + a) whenever n is even ⇒ (10690−4990) is divisible by both 57 and 155 57 = 19 x 3 155 = 31 x 5 ∴ (10690−4990) will be divisible by (19 x 31) = 589 as well. Also, note that (10690−4990) will be odd and options (b) and (c) are even. Hence, they can be rejected