Given that the roots of the equation differ by 2, find the possible values of the constant a. Hence, find the possible values of the roots of the equation.

This is my solution:

____(1)

____(2)

From (1),

____(3)

Sub (3) into (2),

Hence, I got the answer a = -4 or a = 2 but in the book the answers are a = 6 or a = -2. Where have I gone wrong?