College

**Activity 6.2: The Return of the Box**

Earlier, we learned we can make a box from a piece of paper by cutting squares of side length [tex]$x$[/tex] from each corner and then folding up the sides. Let's say we now have a piece of paper that is 8.5 inches by 14 inches. The volume [tex]$V$[/tex], in cubic inches, of the box is a function of the side length [tex]$x$[/tex] where

[tex] \[ V(x) = (14 - 2x)(8.5 - 2x)(x). \] [/tex]

1. Identify the degree and leading term of the polynomial. Explain or show your reasoning.
2. Without graphing, what can you say about the horizontal and vertical intercepts of the graph of [tex]$V$[/tex]? Do these points make sense in this situation?

Answer :

Sure, let's break down the problem step by step.

### Given Information

We have a piece of paper that is 8.5 inches by 14 inches. We cut squares of side length [tex]\( x \)[/tex] from each corner and fold up the sides to form a box. The volume [tex]\( V(x) \)[/tex] of the box is given by:

[tex]\[ V(x) = (14 - 2x)(8.5 - 2x)x \][/tex]

We need to:

1. Identify the degree and leading term of the polynomial [tex]\( V(x) \)[/tex].
2. Discuss the horizontal and vertical intercepts of the graph of [tex]\( V(x) \)[/tex] and verify if they make sense in this context.

### Question 1: Degree and Leading Term

To identify the degree and leading term:

1. Expand the polynomial [tex]\( V(x) \)[/tex]

[tex]\[ V(x) = (14 - 2x)(8.5 - 2x)x \][/tex]

First, multiply the two binomials:

[tex]\[ (14 - 2x)(8.5 - 2x) \][/tex]

[tex]\[ = 14 \cdot 8.5 - 14 \cdot 2x - 2x \cdot 8.5 + 2x \cdot 2x \][/tex]

[tex]\[ = 119 - 28x - 17x + 4x^2 \][/tex]

[tex]\[ = 119 - 45x + 4x^2 \][/tex]

Now, multiply this result by [tex]\( x \)[/tex]:

[tex]\[ V(x) = (119 - 45x + 4x^2)x \][/tex]

[tex]\[ = 119x - 45x^2 + 4x^3 \][/tex]

2. Identify the degree of the polynomial

The degree is the highest power of [tex]\( x \)[/tex]. Here, the highest power is [tex]\( x^3 \)[/tex], so the degree of the polynomial is 3.

3. Determine the leading term

The leading term is the term with the highest power of [tex]\( x \)[/tex]. In this case, it is [tex]\( 4x^3 \)[/tex].

### Answer to Question 1:

- The degree of the polynomial [tex]\( V(x) \)[/tex] is 3.
- The leading term is [tex]\( 4x^3 \)[/tex].

### Question 2: Horizontal and Vertical Intercepts

1. Horizontal intercepts (where [tex]\( V(x) = 0 \)[/tex])

To find the horizontal intercepts, solve [tex]\( V(x) = 0 \)[/tex]:

[tex]\[ (14 - 2x)(8.5 - 2x)x = 0 \][/tex]

Setting each factor to zero gives:

[tex]\[ x = 0 \][/tex]

[tex]\[ 14 - 2x = 0 \implies x = 7 \][/tex]

[tex]\[ 8.5 - 2x = 0 \implies x = 4.25 \][/tex]

So, the horizontal intercepts are at [tex]\( x = 0 \)[/tex], [tex]\( x = 4.25 \)[/tex], and [tex]\( x = 7 \)[/tex].

2. Vertical intercept (at [tex]\( x = 0 \)[/tex])

Substitute [tex]\( x = 0 \)[/tex] into [tex]\( V(x) \)[/tex]:

[tex]\[ V(0) = (14 - 2 \times 0)(8.5 - 2 \times 0)(0) = 0 \][/tex]

So, the vertical intercept is at [tex]\( (0, 0) \)[/tex].

### Do these points make sense in this situation?

- [tex]\( x = 0 \)[/tex]: This means no squares are cut out, so the box does not exist. Thus, it makes sense to have [tex]\( V(0) = 0 \)[/tex].

- [tex]\( x = 4.25 \)[/tex]: This value is within the range that can physically be cut from the corners (since [tex]\( 4.25 < 8.5/2 = 4.25 \)[/tex] and [tex]\( 4.25 < 14/2 = 7 \)[/tex]). Thus, this makes sense.

- [tex]\( x = 7 \)[/tex]: This value is not really practical because cutting squares of side length 7 inches from an 8.5-inch wide sheet means we have no material left to form the box's height. This value is purely theoretical and results in zero volume because the dimensions intersect and collapse.

### Answer to Question 2:

- Horizontal intercepts: [tex]\( x = 0 \)[/tex], [tex]\( x = 4.25 \)[/tex], and [tex]\( x = 7 \)[/tex]; these points represent the situations where the volume of the box is zero.
- Vertical intercept: At [tex]\( x = 0 \)[/tex], [tex]\( V(0) = 0 \)[/tex], indicating no box can be formed if no material is removed from the corners.