Expand this equation (x+delta x) ^3

 x^3 + 3 x^2 delta-X + 3 x delta-X^2 + (delta-X)^3
(x + delta-X)^3 = (x + delta-X)^2 (x + delta-X) 
= (x^2 + 2 x delta-X + delta-X^2) (x + delta-X) 
= (x^2 + 2x delta-X + delta-X^2) * x + (x^2 + 2x delta-X + delta-X^2) * delta-X 
= x^3 + 2x^2 delta-X + x delta-X^2 + x^2 delta-X + 2x delta-X^2 + delta-X^3 
= x^3 + 3x^2 delta-X + 3 x delta-X^2 + delta-X^3 
(nC0) a^n + (nC1) a^(n-1) b + (nC2) a^(n-2) b^2 + ... (nCn-1) a b^(n-1) + (nCn) b^n