Х² - у² + х - у = (х - у)(x+y) + 1(x - y) = (x - y)(x + y + 1)
4a²- 4ab + b² - 9 = ( (2a)² - 2*2a * b + b² ) - 9 =
= ( 2a - b)² - 3² = (2a - b - 3) (2a - b + 3)
ac⁴ - c⁴ - ac² + c² = c²(ac² - c² - a + 1) =
= c² ( c²(a - 1) - 1(a - 1) ) = c² (a - 1)(c² - 1) =
= c²(a - 1)(c² - 1²) = c²(a - 1)(c - 1)(c + 1)
4 - a² + 2ab - b² = - ( - 4 + a² - 2ab + b²) =
= - ( (a² - 2ab + b²) - 2²) = - ( (a - b)² - 2² ) =
= - (a - b - 2)(a - b + 2)