Question

Cho \(x + y = 3\) và \(xy = 2\). Tính \({x^3} + {y^3}\)

Answer 1

\(x^3+y^3=\left(x+y\right)\left(x^2-xy+y^2\right)=\left(x+y\right)\left(x^2+2xy+y^2-3xy\right)\\ =\left(x+y\right)\left[\left(x+y\right)^2-3xy\right]\)

Thay \(x+y=3;xy=2\)

\(=3.\left(3^2-3.2\right)=9\)