2 (X-Y) + 1 / 2A & # (Y-X) factorization

2 (X-Y) + 1 / 2A & # (Y-X) factorization

=2(x-y)-1/2a²(x-y)
=1/2(x-y)(4-a²)
=1/2(x-y)(2+a)(2-a)