a) (x² - xy + y²)(x + y); 6) (a + x)(a² + ax + x²);

a) $$(x^2 - xy + y^2)(x + y) = x^3 + x^2y - x^2y - xy^2 + xy^2 + y^3 = x^3 + y^3$$

б) $$(a + x)(a^2 + ax + x^2) = a^3 + a^2x + ax^2 + a^2x + ax^2 + x^3 = a^3 + 2a^2x + 2ax^2 + x^3$$

Ответ: a) $$x^3 + y^3$$, б) $$a^3 + 2a^2x + 2ax^2 + x^3$$