1) 3m - 3n + (m - n)² = 3(m - n) + (m - n)² = (m - n)(3 + m - n)
2) x + y + x² - y² = (x + y) + (x² - y)² = (x + y) + (x + y)(x - y) = (x + y)(1 + x - y)
3) 9m² + 6mn + n² - 25 = (9m² + 6mn + n²) - 25 = (3m + n)² - 5² =
= (3m + n - 5)(3m + n + 5)
4) ac⁵ - c⁵ - ac³ + c³ = (ac⁵ - c⁵) - (ac³ - c³) = c⁵(a - 1) - c³(a - 1) = (a - 1)(c⁵ - c³)=
c³(c² - 1)(a - 1) = c³(c - 1)(c + 1)(a - 1)