(x² - 2y)² - (1 - 2y)²
[(x² - 2y) + (1 - 2y)][(x² - 2y) - (1 - 2y)]
= (x² - 4y + 1)(x² - 1)
= (x² - 4y + 1)(x + 1)(x - 1)
x² - 9y² + 2x - 6y
= (x² - (3y)²) + 2(x - 3y)
= (x - 3y)(x + 3y) + 2(x - 3y)
= (x - 3y)(x + 3y + 2)