6) а^2 - 9 - 2(a^3 + 27) = а^2 - 9 - 2a^3 - 54 = -2а^3 + а^2 - 63
7) 5b(b^2 - 4) + 2(b^3 - 8) = 5b(b + 2)(b - 2) + 2(b - 2)(b^2 + 2b + 4)= (b - 2)(5b(b + 2) + 2(b^2 + 2b + 4))= (b - 2)(5b^2 + 10b + 2b^2 + 4b + 8)= (b - 2)(7b^2 + 14b + 8)= (b - 2)(7b^2 + 2b + 12b + 8)= (b - 2)(b + 2)(7b + 4)
6) а^2 - 9 - 2(a^3 + 27) = а^2 - 9 - 2a^3 - 54 = -2а^3 + а^2 - 63
7) 5b(b^2 - 4) + 2(b^3 - 8) = 5b(b + 2)(b - 2) + 2(b - 2)(b^2 + 2b + 4)
= (b - 2)(5b(b + 2) + 2(b^2 + 2b + 4))
= (b - 2)(5b^2 + 10b + 2b^2 + 4b + 8)
= (b - 2)(7b^2 + 14b + 8)
= (b - 2)(7b^2 + 2b + 12b + 8)
= (b - 2)(b + 2)(7b + 4)