If $x^4 + x^2y^2 + y^4 = 133$ and $x^2 - xy + y^2 = 7$, then what is the value of xy?
Answer & explanation
Correct answer: option 4
If $x^4 + x^2y^2 + y^4 = 133$
$x^2 - xy + y^2 = 7$--- (1)
what is the value of xy?
x4 + x2y2 + y4 = (x2 – xy + y2) (x2 + xy + y2)
Then , $x^2 + xy + y^2 = \frac{133}{7}$ = 19----- (2)
From equation 1 and 2 we get,
xy = 6