Question

1) (a+b)^3
2) (x-3y)^3

Answer 1

$\displaystyle \tt 1) \: (a+b)^3=\bold{a^3+3a^2b+3ab^2+b^3}\\\displaystyle \tt 2) \: (x-3y)^3=x^3-3x^2\cdot3y+3x\cdot(3y)^2-(3y)^3=x^3-9x^2y+3x\cdot9y^2-27y^3=\bold{x^3-9x^2y+27xy^2-27y^3}$