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Q12.

Expert-verifiedFound in: Page 735

Book edition
Student Edition

Author(s)
Carter, Cuevas, Day, Holiday, Luchin

Pages
801 pages

ISBN
9780078884801

**Carl’s father is building a tool chest that is shaped like a rectangular prism. He wants the tool chest to have a surface area of 62 square feet. The height of the chest will be 1 foot shorter than the width. The length will be 3 feet longer than the height.**

** **

**a. Sketch the model to represent the model.**

**b. Write a polynomial that represents the surface area of the tool chest.**

**c. What are the dimensions of the tool chest?**

a. The model to represent the model is:

b. The polynomial that represents the surface area of the tool chest is $2\left(3{x}^{2}+2x-2\right)$.

c. The dimensions of the tool chest are Length is 5 feet, height is 2 feet and width is 3 feet.

Let the length of the rectangular prism be $l$, width be $w$ and height be $h$.

Since height is 1 foot shorter than width, therefore, the height of rectangular prism in terms of width is $h=w-1$. Similarly, length is 3 feet longer than height, therefore, the length of a rectangular prism in terms of width is

$l=h+3\phantom{\rule{0ex}{0ex}}=\left(w-1\right)+3\phantom{\rule{0ex}{0ex}}=w+2$.

Draw the figure in terms of width.

The formula for the surface area of a rectangular prism is given by $SA=2\left(lh+hw+wl\right)$, where $l$ is the length, $h$ is the height, and $w$ is the width.

Let $x$ be the width, then the height will be $x-1$ and length will be $x+2$. Substitute these values of $w,h$ and $l$ into the equation $A=lh+hw+wl$

role="math" localid="1648023407780" $SA=2\left(lh+hw+wl\right)\phantom{\rule{0ex}{0ex}}=2\left(\left(x+2\right)\left(x-1\right)+\left(x-1\right)x+x\left(x+2\right)\right)$

Simplify the equation in order to find the polynomial that represents the surface area of the tool chest.

$SA=2\left(lh+hw+wl\right)\phantom{\rule{0ex}{0ex}}=2\left(\left(x+2\right)\left(x-1\right)+\left(x-1\right)x+x\left(x+2\right)\right)\phantom{\rule{0ex}{0ex}}=2\left({x}^{2}+2x+{x}^{2}-x+{x}^{2}+x-2\right)\phantom{\rule{0ex}{0ex}}=2\left(3{x}^{2}+2x-2\right)$

The polynomial that represents the surface area of the tool chest is $2\left(3{x}^{2}+2x-2\right)$.

The formula for the surface area of a rectangular prism is given by $SA=2\left(lh+hw+wl\right)$, where $l$ is the length, $h$ is the height, and $w$ is the width.

Let $x$ be the width, then the height will be $x-1$ and length will be $x+2$. Substitute these values of $w,h$ and $l$ into the equation localid="1648023988206" $A=lh+hw+wl$.

$SA=2\left(lh+hw+wl\right)\phantom{\rule{0ex}{0ex}}=2\left(\left(x+2\right)\left(x-1\right)+\left(x-1\right)x+x\left(x+2\right)\right)\phantom{\rule{0ex}{0ex}}=2\left({x}^{2}+2x+{x}^{2}-x+{x}^{2}+x-2\right)\phantom{\rule{0ex}{0ex}}=2\left(3{x}^{2}+2x-2\right)$

The polynomial that represents the surface area of the tool chest is $2\left(3{x}^{2}+2x-2\right)$.

It is given that the surface area of the tool chest is 62 square feet.

$2\left(3{x}^{2}+2x-2\right)=62\phantom{\rule{0ex}{0ex}}3{x}^{2}+2x-2=31\phantom{\rule{0ex}{0ex}}3{x}^{2}+2x-33=0\phantom{\rule{0ex}{0ex}}3{x}^{2}+11x-9x-33=0\phantom{\rule{0ex}{0ex}}x\left(3x+11\right)-3\left(3x+11\right)=0\phantom{\rule{0ex}{0ex}}\left(x-3\right)\left(3x+11\right)=0$

Therefore, $x=3,\frac{-11}{3}$. Since width cannot be negative, therefore, $x=3$ is the valid value.

So, Length = $x+2=5$

And, Height = $x-1=2$.

Therefore, the dimensions of the tool chest are Length is 5 feet, height is 2 feet and width is 3 feet.

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