ax^2 - a - x^2 + x = a(x^2 - 1) - x(x - 1)= a(x + 1)(x - 1) - x(x - 1)= (a(x + 1) - x)(x - 1)= (ax + a - x)(x - 1)= (a - 1)(x + 1)(x - 1)
ax^2 - a - x^2 + x = a(x^2 - 1) - x(x - 1)
= a(x + 1)(x - 1) - x(x - 1)
= (a(x + 1) - x)(x - 1)
= (ax + a - x)(x - 1)
= (a - 1)(x + 1)(x - 1)