# Thread: Polynomial inequality - word problem

1. ## Polynomial inequality - word problem

Hi,

I hope someone can help. I'm trying to solve for the following question:

<= "less than or equal to"
>= "greater than or equal to"

These are my steps:
1. I know that the volume of a rectangle is l x w x h - therefore the inequality to the equation must be x(50 - 2x)(30 - 2x) <= 4000, where x represents the height, 50 - 2x represents the width, and 30 - 2x represents the length.
2. Find the roots to the inequality: x = 0, x = 25, and x = 15
3. Create intervals for the corresponding roots: x <= 0, 0 <= x <= 15, 15 <= x <= 25, x >= 25
4. Identify values within those intervals, then sub those intervals within the inequality equation. If the outcome is less than or equal to 4000, then consider this a range of the side lengths. These ranges would represent my solution(s) to this question.

The textbook solution 5 < x < 7.19. My solution is wrong so I would appreciate some guidance on where I went wrong in my steps.

Sincerely,
Olivia

2. ## Re: Polynomial inequality - word problem

2. Find the roots to the inequality: x = 0, x = 25, and x = 15
the correct inequality is $x(50 - 2x)(30 - 2x) > 4000$

roots of the inequality are where $x(50-2x)(30-2x) - 4000 = 0$

the values of $5 < x < 7.19$ yield a volume $\ge 4000 \, cm^3$