Answer:
x^4 - 11·x^2 + 18 = 0
I use Vieta's formulas
-9·(-2) = 18 and -9 + (-2) = -11
(x^2 - 9)·(x^2 - 2) = 0
(x + 3)·(x - 3)·(x + √2)·(x - √2) = 0
