The expression is,
[tex](x-y)^3[/tex]Expanding the expression we get,
[tex](x-y)^3=(x-y)(x-y)^2\ldots.(1)[/tex]We have,
[tex](x-y)^2=x^2-2xy+y^2\ldots..(2)[/tex]Substituting equation 2 in equation 1, we get,
[tex]\begin{gathered} (x-y)^3=(x-y)(x^2-2xy+y^2) \\ \text{ =}x(x^2-2xy+y^2)-y(x^2-2xy+y^2) \\ \text{ =}x^3-2x^2y+xy^2-yx^2+2xy^2-y^3 \\ \text{ =x}^3-y^3+3xy^2-3x^2y \end{gathered}[/tex]