Разложите на множители:

a) 81x³ - x = x(81x² - 1) = x(9x - 1)(9x + 1) = x(9x - 1)(9x + 1)

б) 3y² - 30y + 75 = 3(y² - 10y + 25) = 3(y - 5)² = 3(y - 5)²

в) x - y - 2x² + 2y² = (x - y) - 2(x² - y²) = (x - y) - 2(x - y)(x + y) = (x - y)(1 - 2(x + y)) = (x - y)(1 - 2x - 2y)