Answer
$(-3, 3) $
Work Step by Step
$x^4 - 7x^2 - 18 < 0$
Find the zeros of the expression.
$(x^2 - 9) (x^2 + 2)$
$(x+3)(x-3)(x^2 + 2)$
$x = -3, 3$
Test numbers in between those zero values to determine if the function is negative or positive
(-∞, -3) $(-)(-)(+) = (+)$
(-3, 3) $(+)(-)(+) = (-)$
(3, ∞) $(+)(+)(+)= (+)$
Thus the solution is $(-3, 3) $
