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| Student Learning Objectives: |
|---|
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| | 11 Theory slides |
| | 13 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
When two polynomials are added or subtracted, the result is also a polynomial. What about the product of two polynomials? Consider, for example, the following pair of polynomials. P(x) &= 2x^3-x+5 [0.1cm] Q(x) &= 4(x+2)(x-1) Is it possible to calculate the product of P(x) and Q(x)? Is P(x)* Q(x) also a polynomial? In the affirmative case, what are the degree, the leading coefficient, and the constant term of the resulting polynomial?
Consider a polynomial P(x) written in standard form. P(x) = a_nx^n + a_(n-1)x^(n-1) + ⋯ + a_1x + a_0 Using the Distributive Property, multiply P(x) by a non-zero constant C.
LHS * C=RHS* C
Distribute C
| Polynomial | Degree | Leading Coefficient |
|---|---|---|
| P(x)= a_nx^n + a_(n-1)x^(n-1) + ⋯ + a_1x + a_0 | n | a_n |
| C* P(x) = C* a_nx^n + C* a_(n-1)x^(n-1) + ⋯ + C* a_1x + C* a_0 | n | C* a_n |
Ali is on his school's student council. He is in charge of decorations for an upcoming school dance. He had the following chat with Kevin.
A = l * w From the chat and the diagram made by Kevin, the poster has to be 2 feet shorter and narrower than the wall. Since the wall is 10 feet tall, the poster will be 8 feet tall. The wall is x feet wide, so the width of the poster is x-2 feet.
A polynomial modeling the area of the poster is obtained by substituting the poster's dimensions into the formula for the area. A(x) = (x-2) * 8 ⇓ A(x) = 8x-16 Note that this polynomial gives the area of the poster depending on the width of the wall.
A(x) = 8x - 16 ⇕ A(x) = 8x^1 - 16 The greatest exponent is 1, which means that the degree of the polynomial is 1. The coefficient in front of the term with the greatest exponent is 8. Thus, the leading coefficient is 8.
x= 16
Multiply
Subtract terms
The area of the poster will be 112 square feet.
Different methods can be used to multiply two polynomials. The following three methods are based on the Distributive Property.
The product of two polynomials can be calculated by using the Distributive Property. Consider, for example, the following pair of polynomials. P(x) &= x^3 + 2x^2 - 3 Q(x) &= x^2 + 4 To multiply these two polynomials, the following four steps can be followed.
Distribute x^3 + 2x^2 - 3
a^m*a^n=a^(m+n)
Add terms
Multiply
Commutative Property of Addition
Associative Property of Addition
Add terms
Given two polynomials, their product can be calculated by using a box or table. Consider, for example, the following pair of polynomials. P(x) &= x^3 + 2x^2 - 3 Q(x) &= x^2 + 4 To multiply these two polynomials, the following four steps can be followed.
| Polynomial | Number of Terms |
|---|---|
| P(x) = x^3 + 2x^2 - 3 | 3 |
| Q(x) = x^2 + 4 | 2 |
For example, a table with 3 rows and 2 columns is needed to multiply P(x) by Q(x).
The product of these polynomials has been found to be x^5+2x^4+4x^3+5x^2-12.
The FOIL method is a mnemonic for remembering how to multiply two binomials. The word FOIL is an acronym for the words First, Outer, Inner, and Last. Consider, for example, the following product. (x+6)(3x-2) These two binomials can be multiplied by following five steps.
Commutative Property of Multiplication
a* a=a^2
a(- b)=- a * b
Multiply
Add terms
Diego's parents recently bought a piece of land where they plan to raise pigs. They need to fence off a rectangular pigpen before buying the pigs. A farmer friend told Diego that the dimensions of the pigpen, in yards, vary according to the number of pigs x that are being raised in it.
Length: & 5x+2 Width: & 3x+1 By multiplying the two binomials, a polynomial modeling the pigpen area will be obtained. A(x) = (5x+2)(3x+1) To write A(x) in standard form, the product on the right-hand side can be performed by using the FOIL method.
Consequently, the degree of A(x) is 2 and its leading coefficient is 15.
x= 15
Calculate power and product
Multiply
Add terms
Consequently, to raise 15 pigs, the pigpen must have an area of 3542 square yards.
Consider a right triangle on the coordinate plane with vertices J(-10,0), K(x,0), and L(x,P(x)), where P(x)=x^3 + 3x^2 - 18x + 54.
A = 1/2* JK* KL The length of the legs can be written using the given expressions. JK &= x+10 KL &= x^3 + 3x^2 - 18x + 54 Next, substitute the previous expressions into the formula for the area. A(x)=1/2( x+10)( x^3 + 3x^2 - 18x + 54) For simplicity, the product of the two polynomials will be computed first. Then, the resulting polynomial will be multiplied by 12. To perform the polynomial multiplication, the Box Method can be used. To do so, start by drawing a 2* 4 table and writing the row and column labels.
The next step is to fill the table by multiplying the terms written on the corresponding borders.
Now, add all the terms inside the table and simplify by combining like terms.
Having computed JK* KL, a polynomial modeling the area of △ JKL can be found.
JK* KL= x^4+13x^3+12x^2-126x+540
Distribute 1/2
Consequently, the degree of A(x) is 4 and its leading coefficient is 12.
To find the area of the above triangle, substitute 3 for x into the polynomial A(x) found in Part A.
x= 3
Calculate power and product
Add fractions
Add and subtract terms
Calculate quotient
Add terms
In consequence, when K has coordinates (3,0), the triangle JKL has an area of 351.
To determine which triangle has the larger area, find A(-4) and A(-1) and compare them. Start by finding A(-4).
x= -4
Calculate power and product
Calculate quotient
Add and subtract terms
Next, find the value of A(-1).
x= -1
Calculate power and product
Add fractions
Subtract terms
Calculate quotient
Add and subtract terms
As can be seen, A(-1) is greater than A(-4). Therefore, the triangle generated by K_2(-1,0) has the larger area.
Izabella bought her nephew a bag of magic grow toys for his birthday. Among the toys, there was a trailer and its rectangular container. Initially, the container was 5 centimeters long, 2 centimeters wide, and 3 centimeters high.
The bag says that when the container is placed underwater, its dimensions will increase according to the following functions. The maximum possible size of the container is reached after being underwater for 9 hours. l(t) &= 14t^2 + 5 [0.2cm] w(t) &= - 19t^2 + 2t + 2 [0.2cm] h(t) &= t + 3 Here, t represents the number of hours the toy has been underwater.
V = w * l * h Therefore, to find a polynomial representing the container's volume after passing t hours underwater, multiply the expressions that model the dimensions of the container. w(t) * l(t) * h(t) ⇓ (1/4t^2 + 5) (-1/9t^2 + 2t + 2) (t + 3) By applying the Commutative Property of Multiplication, the previous product can be rewritten to have the two binomials next to each other. (-1/9t^2 + 2t + 2) (1/4t^2 + 5) (t + 3) Then, these two binomials can be multiplied using the FOIL method. For simplicity, the trinomial will not be written during this multiplication.
Finally, the trinomial has to be multiplied by the resulting polynomial. To perform such multiplication the Distributive Property can be used. Here, each term of the trinomial will be distributed to each term of the second polynomial.
Distribute - 19t^2 + 2t + 2
Distribute 14t^3, 34t^2, 5t, & 15
Commutative Property of Multiplication
a^m*a^n=a^(m+n)
Multiply fractions
Simplify quotient and product
Commutative Property of Addition
Add and subtract terms
10:00AM ⟶ 4:00PM_(6 hours) Consequently, to find the current volume of the container, evaluate V(t) at t= 6.
t= 6
Calculate power
a/c* b = a* b/c
Multiply
Calculate quotient
Add and subtract terms
After passing 6 hours underwater, the container will have a volume of 1260 cubic centimeters.
In all the examples seen throughout this lesson, the product of two or more polynomials has resulted in a new polynomial. This is not a coincidence. In fact, the following property guarantees that multiplying polynomials always produces a polynomial.
Given two polynomials P(x) and Q(x), the product P(x)* Q(x) is always a polynomial.
Multiplying two polynomials produces a new polynomial.
In other words, the polynomials are closed under multiplication.
Since P(x) and Q(x) are polynomials, all the exponents are whole numbers. Furthermore, because the whole numbers are closed under addition, the exponents of the resulting expression are whole numbers. Then, the new expression can be rewritten as follows. P(x)Q(x) &= c_kx^D + ⋯ + c_1x + c_0 Consequently, the new expression is a polynomial. Therefore, the product of two polynomials produces a polynomial, which proves that the polynomials are closed under multiplication.
Given two polynomials P(x) and Q(x), compute their product and find the required information.
Before finishing this lesson, take another look at the challenge presented at the beginning. There it was given the following pair of polynomials. P(x) &= 2x^3-x+5 [0.1cm] Q(x) &= 4(x+2)(x-1) In the challenge, it was asked whether it was possible to find the product of P(x) and Q(x). Now, with all the knowledge learned, it can be said that it is possible to multiply these two polynomials, and the resulting expression will also be a polynomial. To compute P(x)* Q(x), first, rewrite Q(x) in standard form. To do so, the FOIL Method can be applied.
Multiply ( x+ 2) by ( x -1)
a^m*a^n=a^(m+n)
a(- b)=- a * b
a * 1=a
Add terms
Distribute 4
Substitute expressions
a^m*a^n=a^(m+n)
Multiply
Commutative Property of Addition
Add and subtract terms
Write a polynomial, in standard form and in terms of π, representing the surface area of the following cylinder.
Let's begin by writing the formula for the surface area of a cylinder. S = 2π r^2 + 2π rh Here, r is the radius of the cylinder and h is the height. From the given diagram, we can see that r=5t-2 and h=3t^2-1. Let's substitute these expressions into the formula.
Finally, we write the power as the product of two binomials and multiply them using the FOIL Method. Since we will leave the polynomial in terms of π, we can continue by factoring out 2π.
The resulting polynomial represents the surface area of the given cylinder.
Diego plans to build a rectangular chicken coop. According to his farmer uncle, the dimensions of the chicken coop depend on the number of hens h that he intends to keep.
Write a polynomial A(h) in standard form that models the chicken coop area.
The area of a rectangle is obtained by multiplying its length by its width. Then, let's start by writing the dimensions suggested by Diego's uncle. Length: & 2h-1 Width: & 4h^2-5h+2 If we multiply the binomial by the trinomial, we will get a polynomial modeling the chicken coop area. A(h) = (2h-1)(4h^2-5h+2) To write A(x) in standard form, let's perform the product on the right-hand side.
The product A(h)=(2h-1)(4h^2-5h+2) can also be expanded using the Box Method. Since the first polynomial has two terms and the second has three terms, we will use a table with 2 rows and three columns.
| * | 4h^2 | -5h | 2 |
|---|---|---|---|
| 2h | |||
| -1 |
Now, let's fill in the table's cells by multiplying the terms written on the corresponding borders of the table.
| * | 4h^2 | -5h | 2 |
|---|---|---|---|
| 2h | 8h^3 | -10h^2 | 4h |
| -1 | -4h^2 | 5h | -2 |
Finally, we add all the expressions inside the table and combine like terms.
Write a polynomial in standard form that represents the volume of the following rectangular prism.
The volume of a rectangular prism is found by multiplying its three dimensions. Therefore, let's start by writing the dimensions of the given solid. Length: & x+2 Width: & x+1 Height: & x-1 If we multiply the three expressions representing the prism's dimensions, we will get a polynomial representing its volume. V(x) = (x+2)(x+1)(x-1) To write V(x) in standard form, let's multiply the three binomials, starting with the two at the left.
To write V(x) in standard form the three binomials can be multiplied following the next steps.
Let's begin with the first step. Here, we need to multiply the first terms of each binomial. ( x+1)( x-1) ⇓ x* x The empty box is there as a reminder that there are still missing terms. Next, we multiply the outer terms. ( x+1)(x- 1) ⇓ x* x - x* 1 Now, it is the turn of the inner terms. (x+ 1)( x-1) ⇓ x* x - x* 1 + 1* x Then, we multiply the last terms. (x+ 1)(x- 1) ⇓ x* x - x* 1 + 1* x - 1* 1 After performing each of the products and combining like terms, it is obtained the following binomial. (x+1)(x-1) = x^2 - 1 Now, the previous binomial will be multiplied by the binomial (x+2). Again, we can use the FOIL method. ( x+2)( x^2-1) ⇓ x* x^2 We continue multiplying the outer terms. ( x+2)(x^2- 1) ⇓ x* x^2 - x* 1 Next, we multiply the inner terms. (x+ 2)( x^2-1) ⇓ x* x^2 - x* 1 + 2* x^2 Finally, we multiply the last terms. (x+ 2)(x^2- 1) ⇓ x* x^2 - x* 1 + 2* x^2 - 2* 1 Once the products are performed it is obtained the following polynomial. V(x) = x^3 + 2x^2 - x - 2
Although there are some missing terms, we do not need them to find the degree of P(x)Q(x). The reason is that when two polynomials are multiplied, the product is a new polynomial whose degree equals the sum of the degrees of the multiplied polynomials. P(x) &= 3x^4 + 6x^2 + ??? - 4 Q(x) &= 5x^2 - ??? + 2 As we can see, the degree of P(x) is 4 and the degree of Q(x) is 2. With this information, we can find the degree of P(x)Q(x). Degree ofP(x)Q(x) 4+ 2 = 6 Consequently, the degree of the product of the given polynomials is 6.
As in Part A, we do not need to know the missing terms to find the leading coefficient of P(x)Q(x). The reason is that when two polynomials are multiplied, the leading coefficient of the resulting polynomial equals the product of the leading coefficients of the multiplied polynomials.
P(x) &= 3x^4 + 6x^2 + ??? - 4
Q(x) &= 5x^2 - ??? + 2
The leading coefficient of P(x) is 3 and the leading coefficient of Q(x) is 5. Let's find their product.
Leading Coefficient ofP(x)Q(x)
3* 5 = 15
The leading coefficient of the product of the given polynomials is 15.
In a similar manner, when two polynomials are multiplied, the constant term of the resulting polynomial equals the product of the constant terms of the multiplied polynomials. Then, we only need to know the constant terms of P(x) and Q(x).
P(x) &= 3x^4 + 6x^2 + ??? - 4
Q(x) &= 5x^2 - ??? + 2
The constant term of P(x) is -4 and the constant term of Q(x) is 2. Let's find their product.
Constant Term ofP(x)Q(x)
-4* 2 = -8
The constant term of the product of the given polynomials is -8.