x + y = 12 Raise both sides to the 3rd power (cube both sides) (x + y)³ = 12³ (x + y)(x + y)(x + y) = 1728 (x + y)(x² + 2xy + y²) = 1728 x³ + 2x²y + xy² + x²y +2xy² + y³ = 1728 x³ + 3x²y + 3xy² + y³ = 1728 Factor 3xy out of the two middle terms: x³ + 3xy(x + y) + y³ = 1728 We substitute 27 for xy and 12 for x + y x³ + 3(27)(12) + y³ = 1728 x³ + 972 + y³ = 1728 x³ + y³ = 756 Edwin
