`a,(a-b)^3+(a+b)^3-2a^3`
`=a^3-3a^2b+3ab^2-b^3+a^3+3a^2b+3ab^2+b^3-2a^3`
`=(a^3+a^3-2a^3)+(-3a^2b+3a^2b)+(3ab^2+3ab^2)+(-b^3+b^3)`
`=6ab^2`
`b,(x+2)^3+(x-2)^3+x^3-3x(x+2)(x-2)`
`=x^3+6x^2+12x+8+x^3-6x^2+12x-8+x^3-3x(x^2-4)`
`=x^3+6x^2+12x+8+x^3-6x^2+12x-8+x^3-3x^3+12x`
`=36x`