Разложим на множители выражения:
1) $$x - 3y + x^2 - 9y^2 = (x - 3y) + (x^2 - (3y)^2) = (x - 3y) + (x - 3y)(x + 3y) = (x - 3y)(1 + x + 3y)$$.
2) $$9m^2 + 6mn + n^2 - 25 = (9m^2 + 6mn + n^2) - 25 = (3m + n)^2 - 5^2 = (3m + n - 5)(3m + n + 5)$$.
3) $$ab^5 - b^5 - ab^3 + b^3 = b^5(a - 1) - b^3(a - 1) = (a - 1)(b^5 - b^3) = b^3(a - 1)(b^2 - 1) = b^3(a - 1)(b - 1)(b + 1)$$.
4) $$1 - x^2 + 10xy - 25y^2 = 1 - (x^2 - 10xy + 25y^2) = 1 - (x - 5y)^2 = (1 - (x - 5y))(1 + (x - 5y)) = (1 - x + 5y)(1 + x - 5y)$$.
Ответ:
1) $$(x - 3y)(1 + x + 3y)$$;
2) $$(3m + n - 5)(3m + n + 5)$$;
3) $$b^3(a - 1)(b - 1)(b + 1)$$;
4) $$(1 - x + 5y)(1 + x - 5y)$$.