Question

If x + y = 3 and xy = 2, then the value of $x^3-y^3$ is equal to

• A. 6
• B. 7
• C. 8
• D. 0

Answer 1

The correct option is B 7

Formula used:
$x^3-y^3=(x-y)(x^2+xy+y^2)$
$=\left(\sqrt{(x+y{)}^2-4xy}\right)\left[\right(x+y{)}^2-xy]$
$=\left(\sqrt{(3{)}^2-4(2)}\right)\left[\right(3{)}^2-2]$
$=\left(\sqrt{1}\right)\left(7\right)=7$
Option B is correct.