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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
Tadeo invited his friends to watch the Champions League final next Sunday. He plans to meet in the backyard and wants to project the game on a wall of the house using a video beam. However, on Saturday night, Tadeo made a test and the image did not look so clear, so he decided to buy a projector screen.
The diagram shows the dimensions of the wall. Write a polynomial function P(x) that models the area of the projector screen in standard form.
Because the projector screen has a rectangular shape, its area equals its length multiplied by its width. A = l * w From the diagram, we can see that the projector screen is 1.25 feet shorter and narrower from each side of the wall. The wall is 12 feet tall, so we can find the height of the screen by subtracting 1.25 feet from each side. 12-1.25-1.25=9.5 We can find the width of the screen in a similar way. x-1.25-1.25=x-2.5 Let's look at these dimensions in the diagram!
A polynomial modeling the area of the projector screen is obtained by substituting its dimensions into the formula for the area. P(x) = (x-2.5)(9.5) ⇕ P(x) = 9.5x-23.75 Note that this polynomial gives the area of the projector screen depending on the width of the wall. The polynomial can also be written using fractions instead of decimal numbers. To do this, we expand the corresponding terms.
Let's find the required product using the Distributive Property. To start, we distribute the left-hand side binomial to each term of the right-hand side binomial. ( x-4)( x+2) ⇓ ( x-4) x+( x-4) 2 Next, we apply the Distributive Property once more to clear the parentheses and continue combining like terms to simplify the resulting expression.
To find the second product, we will use the FOIL Method. Remember, the word FOIL stands for First, Outer, Inner, and Last.
With this in mind, we can proceed with the required multiplication. Let's start by multiplying the first terms. ( y-3)( y+3) ⇓ y* y The empty box is there as a reminder that there are still missing terms. Next, we multiply the outer terms. ( y-3)(y+ 3) ⇓ y* y + y* 3 Now, it is the turn of the inner terms. (y- 3)( y+3) ⇓ y* y + y* 3 - 3* y Then, we multiply the last terms. (y- 3)(y+ 3) ⇓ y* y + y* 3 - 3* y - 3* 3 Finally, we perform each of the products and combine like terms to simplify the resulting polynomial.
For the third product, let's use the Box Method. First, we determine the dimensions of the table. To do this, let's count the number of terms in each polynomial. ccc Polynomial & & Number of Terms [0.1cm] (z+2) & & 2 [0.1cm] (1-z) & & 2 Since each polynomial has two terms, we will need a table with two rows and two columns. However, we will add an extra row and column to write the terms of each polynomial. Let's write the terms of the first polynomial in the first column and the terms of the second polynomial in the first row.
| * | 1 | - z |
|---|---|---|
| z | ||
| 2 |
Next, we fill in the table's cells by multiplying the terms written on the corresponding borders of the table.
| * | 1 | - z |
|---|---|---|
| z | z(1) | z(- z) |
| 2 | 2(1) | 2(- z) |
Finally, let's add all the expressions inside the table and combine like terms.
To start, let's write the formula for finding the area of a rectangle. A = l * w In our case, the rectangle has dimensions 3x+1 and x-4. Let's substitute them into the formula. A(x) = (3x+1)(x-4) Finally, we write the previous polynomial in standard form by multiplying the two binomials.
The last polynomial represents the area of the given rectangle.
We are interested in finding the area of the given triangle. Therefore, let's begin by writing the formula that we will use.
A = 1/2bh
Since the given triangle is a right triangle, we can use the legs to find the area — that is, b=4g+1 and h=9g-2. Let's substitute these expressions into the formula.
A(g) = 1/2(4g+1)(9g-2)
To write the polynomial A(g) in standard form, we can multiply the two binomials using the FOIL Method.
Note that the area of the shaded region is the area of the rectangle minus the area of the square. A_(Shaded) = A_R - A_S Let's start by finding the area of the rectangle. To do this, we multiply its dimensions.
Next, let's find the area of the square.
Finally, let's subtract the square's area from the rectangle's area.
The obtained polynomial represents the area of the given shaded region.
Let's recall the formula for the surface area of a cube. SA =6l ^2 Here l is the side length of the cube. In our case l= 2k+1. Let's substitute this expression into the formula. A(k)=6( 2k+1)^2 Now, let's simplify the obtained expression and write it in standard form.
We can multiply the binomials using the FOIL Method. Recall that the word FOIL stands for First, Outer, Inner, and Last.
Finally, we combine like terms to simplify the polynomial.
The surface area of the given cube is represented by A(k)=24k^2 + 24k + 6.
Let's disassemble the given rectangular prism to see the faces individually.
With this in mind, we can write an expression representing the surface area of the prism. SA = 2A_1 + 2A_2 + 2A_3 ⇓ SA = 2(A_1 + A_2 + A_3) Let's start by finding the area of the bases, whose dimensions are 2p and 3p+1.
In a similar way, let's find the area of the lateral face with dimensions 3p+1 and 9p-5.
Next, let's find the area of the lateral face with dimensions 2p and 9p-5.
Now we are ready to find the polynomial representing the surface area of the rectangular prism. To do this, we substitute the expressions we found for A_1, A_2, and A_3.
According to the box method, the top row labels are the terms of one of the polynomials being multiplied. Similarly, the elements at the left of the table form the other polynomial. Let's start by writing the polynomials being multiplied. P(x) &= x^2-2x+6 Q(x) &= 2x^2+3 Now, the cells of the table are filled by multiplying the terms written on the corresponding borders of the table. For example, the top-left cell corresponds to the product of 2x^2 and x^2.
In a similar fashion, the second cell of the second row corresponds to the product of 3 and -2x.
Knowing this, we can find A and B. A &= 2x^2* x^2 = 2x^4 B &= 3(-2x) = -6x Finally, we add the two previous expressions. A+B = 2x^4 - 6x
Now that we know the expressions for A and B, let's begin by writing the in the table.
The result of the polynomial multiplication is the sum of all the expressions inside the table. Therefore, let's add them and combine like terms, if any.
The degree of a polynomial is the highest exponent in the polynomial. Therefore, let's start by finding R(x).
From the resulting polynomial, we can see that the highest exponent is 9. Therefore, the degree of R(x) is 9.
The leading coefficient of a polynomial is the coefficient in front of the term with the highest exponent. Knowing this, let's highlight the leading coefficients of P(x), Q(x), and R(x).
P(x) &= 2x^3-5
Q(x) &= 4x^6+2
R(x) &= 8x^9 - 20x^6 + 4x^3 - 10
The leading coefficients of P(x), Q(x), and R(x) are 2, 4, and 8, respectively. Let's find the required sum using this information!
2 + 4 + 8 = 14
The constant term of a polynomial is the term with no variables including its sign.
R(x) = 8x^9 - 20x^6 + 4x^3 - 10
Therefore, the constant term of R(x) is -10.