If x + y + 3 = 0, then find the value of $x^3 + y^3 -9xy +9$.
Answer & explanation
Correct answer: option 1
If x + y + 3 = 0
then , x + y = -3
cubing on both side=
( x + y)3 = (-3)3
x3 + y3 + 3xy(x + y) = -27
x3 + y3 + 3xy(-3) = -27
x3 + y3 + -9xy = -27
then, $x^3 + y^3 -9xy +9$ = $-27 +9$ = -18