028.39. a) \((b - 5)(b + 5)(b^2 + 25)\); б) \((3 - y)(3 + y)(9 + y^2)\); в) \((a - 2)(a + 2)(a^2 + 4)\); г) \((c^2 - 1)(c^2 + 1)(c^4 + 1)\)

**28.39** * **a)** \((b - 5)(b + 5)(b^2 + 25) = (b^2 - 25)(b^2 + 25) = b^4 - 625\) * **б)** \((3 - y)(3 + y)(9 + y^2) = (9 - y^2)(9 + y^2) = 81 - y^4\) * **в)** \((a - 2)(a + 2)(a^2 + 4) = (a^2 - 4)(a^2 + 4) = a^4 - 16\) * **г)** \((c^2 - 1)(c^2 + 1)(c^4 + 1) = (c^4 - 1)(c^4 + 1) = c^8 - 1\)