a^3+-b^3=(a+-b)(a^2-+ab+b^2)
(a-2)(a^2+2a+4)-(a+c)(a^2-ac+c^2)+(c+2)(c^2-2c+4)=(a^3-2^3)-(a^3+c^3)+(c^3+2^3)= a^3-8 - a^3 - c^3 + c^3 + 8 = a^3 - a^3 -8 + 8 - c^3 + c^3 = 0
a^3+-b^3=(a+-b)(a^2-+ab+b^2)
(a-2)(a^2+2a+4)-(a+c)(a^2-ac+c^2)+(c+2)(c^2-2c+4)=(a^3-2^3)-(a^3+c^3)+(c^3+2^3)= a^3-8 - a^3 - c^3 + c^3 + 8 = a^3 - a^3 -8 + 8 - c^3 + c^3 = 0