multiply

1) (x-3)^3.

2) (2x+y)^3.

3) (3a-2)^3

(x-3)(x-3)= (x^2-6x+9)

(x^2-6x+9)(x-3)= x^3-6x^2+9x-3x^2+18x-27
Add Like Terms

x^3-9x^2+27x-27

The same idea for the others.