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We can make a box from a piece of paper that is 8.5 inches by 14 inches by cutting squares of side length from each corner and then folding up the sides. The volume , in cubic inches, of the box is a function of the side length , where .
If students are unsure how to identify the degree or leading term of the polynomial written in factored form, consider asking:
The goal of this discussion is for students to consider the advantages and disadvantages of polynomials written in factored form and standard form, and to see different ways to organize the use of the distributive property.
Display the function from the Task Statement for all to see. Invite previously selected students to share how they determined the degree and leading term of the polynomial. Here are some possible questions for discussion:
If not brought up in students' explanations, display the function for all to see. Ask students which form of the polynomial, factored form or standard form, makes it easier to identify the following features:
If time allows, display a set of scaled axes and add these features to the display. Then sketch in the cubic curve of at the conclusion as a small preview of the work students will do in future lessons investigating the general shape of polynomials with different degrees.
Use the following examples and diagrams as necessary.
| 2 | ||
|---|---|---|
| 3 | 6 |
| 12 |
Use the distributive property to show that each pair of expressions is equivalent.
Invite students to share their diagrams. If some students used methods other than diagrams to multiply the expressions, invite them to share and explain their method.
Arrange students in groups of 2. Graphing technology is needed for every student. Display the two functions for all to see and ask students to predict how the graphs of each function will be the same or different. If necessary to save time, assign each partner either or to rewrite in the second question.
The purpose of this discussion is for students to understand that multiplying by a constant causes all output values of a function to be times farther from the horizontal axis, which in turn means has no effect on the zeros of a function.
Begin the discussion by selecting 2–3 students to share how they rewrote and in standard form. If necessary, remind students how multiplying in a different order results in the same product.
Ask students, “How can you identify the constant term without multiplying out the entire expression?” (With an expression like , the constant term is 21 and comes from .)
If not brought up during the discussion, it is important to note that all three polynomials have the same degree and the same zeros, yet the three have distinct outputs for all other inputs. The idea that knowing the degree and zeros of a polynomial is insufficient for identifying a specific polynomial will be revisited in future lessons. If time allows, ask students to write an equation for a fourth function with the same degree and zeros as the first three.
Let and .