(2a-b)^3-(2a+b)^3=(4a2-4ab+b2)(2a-b)-(4a2+4ab+b2)(2a+b)=
=(8a3-8a2b+2ab2-4a2b+4ab2-b3)-(8a3+8a2b+2ab2+4a2b+4ab2+b3)=
=8a3-12a2b+6ab2-b3-8a3-12a2b-6ab2-b3=-24a2b-2b3=
=-2b(12a^2+b^2)
(2a-b)^3-(2a+b)^3=(4a2-4ab+b2)(2a-b)-(4a2+4ab+b2)(2a+b)=
=(8a3-8a2b+2ab2-4a2b+4ab2-b3)-(8a3+8a2b+2ab2+4a2b+4ab2+b3)=
=8a3-12a2b+6ab2-b3-8a3-12a2b-6ab2-b3=-24a2b-2b3=
=-2b(12a^2+b^2)