Answer:
[tex](x - y) ^{3} - 8 {(x + y)}^{3} \\ \\ ( {x}^{3} - 3 {x}^{2} y + 3x {y}^{2} - {y}^{3}) - 8( {x}^{3} + 3 {x}^{2} y + 3x {y}^{2} + {y}^{3} ) \\ \\ ( {x}^{3} - 3 {x}^{2} y + 3x {y}^{2} - {y}^{3}) + ( - 8 {x}^{3} - 24 {x}^{2} y - 24x {y}^{2} - 8 {y}^{3} ) \\ \\ \\ = - 7 {x}^{3} - 27 {x}^{2} y - 21x {y}^{2} - 9 {y}^{3} [/tex]
I hope I helped you^_^
