а) $$(x^2 - 5)(x^2 + 5) = (x^2)^2 - 5^2 = x^4 - 25$$
б) $$(4 + y^2)(y^2 - 4) = (y^2 + 4)(y^2 - 4) = (y^2)^2 - 4^2 = y^4 - 16$$
e) $$(a^3 - b^2)(a^3 + b^2) = (a^3)^2 - (b^2)^2 = a^6 - b^4$$
ж) $$(c^4 + d^2)(d^2 - c^4) = (d^2 + c^4)(d^2 - c^4) = (d^2)^2 - (c^4)^2 = d^4 - c^8$$