А) (a^2 - b^2) : (a + b) = (a - b)(a + b) : (a + b) = a - b.
б) (a^4 - b^4) : (a - b) = (a^2 - b^2)(a^2 + b^2) : (a - b) = (a - b)(a + b)(a^2 + b^2) : (a - b) = (a + b)(a^2 + b^2).
в) (y^6 - x^6) : (x^2 + xy + y^2) = (y^3 - x^3)(y^3 + x^3) : (x^2 + xy + y^2) = (y - x)(x^2 + xy + y^2)(y^3 + x^3) : (x^2 + xy + y^2) = (y - x)(y^3 + x^3).