### Friday, July 29, 2016

#### If x+y = x y = 3, then what is x^3 + y^3?

If x+y = x y = 3, then what is x^3 + y^3? Solution 1: 27 = (x+y)^3 = x^3 + 3 x^3 y + 3 x y^2 + y^3 = (x^3 + y^3) + 3 x y (x+y) = (x^3 + y^3) + 3 * 3 * 3 = (x^3 + y^3) + 27 Therefore x^3 + y^3 = 0 Solution 2: x+y = x y = 3 (t-x)(t-y) = t^2 - (x+y) t + x y The quadratic equation, t^2 - (x+y) t + x y =...

**Sign in** to see full entry.