Question

Solve the inequality. Write your answer using interval notation. X(x − 1)(x + 4) > 0

Answer 1

Set each factor EQUAL to zero to find the zeroes (since it is not actually equal to zero, you will use an open circle when graphing and an open bracket when writing in interval notation).

x = 0           x-1 = 0             x + 4 = 0

                   x = 1                x = -4

Next, choose a value to the far left, between each of the zeroes, and to the far right to evaluate if it makes a true statement when input into the given inequality.

far left (I choose -5): -5(-5 - 1)(-5 + 4) > 0   →  (-)(-)(-) > 0  →   negative > 0  FALSE

- 4 to 0 (I choose -2): -2(-2 - 1)(-2 + 4) > 0   →  (-)(-)(+) > 0  →   positive > 0  TRUE

0 to 1 (I choose 0.5): .5(.5 - 1)(.5 + 4) > 0   →  (+)(-)(+) > 0  →   negative > 0  FALSE

far right (I choose 2): 2(2 - 1)(2 + 4) > 0   →  (+)(+)(+) > 0  →   positive > 0  TRUE

Answer: (-4, 0) U (1, ∞)