Question

A rectangular box has the dimensions shown in the diagram. The volume of the box is given by the function V(x) = x3 – 4x, where x is the height in inches.
What is the height of the box if the volume is 15 in.3?


There is a rectangular box with length x+2 in. , width x-2 in. , and height x in.


height = in.

Answer 1

Answer:

$Height =3$

Step-by-step explanation:

Given

$Length = x + 2$

$Width = x - 2$

$Height = x$

$Volume = 15$

Required

Find the height

The volume is calculated as thus:

$Volume = Length * Width * Height$

This gives

$15 = (x + 2) * (x - 2) * x$

Apply difference of two squares

$15 =(x^2 - 4 ) * x$

$15 = x^3 - 4x$

Subtract 15 from both sides

$x^3 - 4x - 15 = 0$

Using a calculator to factorize, we have:

$(x-3)(x^2+3x+5) = 0$

Split

$x - 3 = 0$ or $x^2 + 3x + 5 = 0$

$x = 3$ or  $x^2 + 3x + 5 = 0$

x has complex roots for $x^2 + 3x + 5 = 0$

Hence:

$x = 3$

Recall that:

$Height = x$

$Height =3$