Question

If $(x + y) = 3$ and $xy = 2$, then what is the value of $x^3 + y^3$?

Accepted Answer

D. We know $x^3 + y^3 = (x + y)^3 - 3xy(x + y)$. Substitute $(x + y) = 3$ and $xy = 2$: $x^3 + y^3 = 3^3 - 3(2)(3) = 27 - 18 = 9$.

Sum of Cubes Identity

Practise this under exam conditions