We know that, \( \Large \left(x + y\right)^{3} = x^{3} + y^{3} + 3xy \left(x + y\right) \) \( \Large 1 = x^{3} + y^{3} + 3xy \) [given, x + y = 1] => \( \Large x^{3} + y^{3} + 3xy = 1 \)
