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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Teacher Road Map for Lesson 21: The Remainder Theorem
Objective in Student Friendly Language:
Today I am: comparing the graph of a polynomial to division of a factor
So that I can: understand how the remainder can be used to find specific points on a polynomial graph.
Iโll know I have it when I can: write a polynomial function bases on the roots and y-intercept.
Flow: o Students examine a polynomial functionโs graph and equation to determine roots. They then
divide the polynomial by various binomials to see the relationship between the remainder and the point on the graph.
o Students review what they learned in Unit 1 to graph a 4th degree polynomial function given one root and refine their graph using the ideas of the Remainder Theorem.
o Students state the Remainder Theorem and then practice using it. o Students write an equation of a polynomial function based on the graph, roots and y-
intercept. Big Ideas:
o The Remainder Theorem is extremely useful for finding specific values of a polynomial function and for further defining graphs of polynomials. In later math courses, the Remainder Theorem helps limit the domain in calculus problems.
CCS Standards:
o A-APR.2 Know and apply the Remainder Theorem: For a polynomial f(x) and a number a, the remainder on division by x โ a is p(a), so p(a) = 0 if and only if (x โ a) is a factor of p(x).
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Student Outcomes Students know and apply the remainder theorem and understand the role zeros play in the theorem.
Lesson Notes
In this lesson, students are primarily working on exercises that lead them to the concept of the remainder theorem, the connection between factors and zeros of a polynomial, and how this relates to the graph of a polynomial function. Students should understand that for a polynomial function ๐๐ and a number ๐๐, the remainder on division by ๐ฅ๐ฅ โ ๐๐ is the value ๐๐(๐๐) and extend this to the idea that ๐๐(๐๐) = 0 if and only if (๐ฅ๐ฅ โ๐๐) is a factor of the polynomial (A-APR.2). There should be plenty of discussion after each exercise.
Exploratory Exercise 1. Consider the polynomial ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐๐๐๐๐๐๐ โ ๐๐๐๐๐๐ + ๐๐๐๐๐๐
shown graphed on the right. A. Is ๐๐ a zero of the polynomial ๐ท๐ท? How do you know?
No, f(1) โ 0. OR No, the function does not cross or touch the x-axis at x = 1.
B. Divide P(x) by x โ 1. You may use any method (long division,
reserve tabular method or synthetic division). What is the remainder?
The remainder is 84. C. What is f(1)? How does this answer compare to the remainder
in Part B?
f(1) = 84. They are the same. D. Is ๐๐ + ๐๐ one of the factors of ๐ท๐ท? How do you know?
Yes x + 3 is a factor of P since the function crosses the x-axis at -3. E. Divide P(x) by x + 3. What is the remainder?
P(x) รท (x + 3) = x3 โ 28x + 48. The remainder is 0. F. What is f(-3)? How does this answer compare to the remainder in Part E?
f(-3) = 0. They are the same.
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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2. The polynomial function, 4 3 2( ) 7 6f x x x x x= + โ โ + , has a zero at -3. Graph the function on the grid at the right.
A. Use what you learned in Exercise 1 and your knowledge of
polynomials from Unit 1 to create an accurate graph of the function. B. What is the value of f(-2)? Mark this point on your graph.
f(-2) = -12. C. What is the value of f(0)? Mark this point on your graph.
f(0) = 6. D. What is the value of f(-4)? Can this be marked on your graph?
f(-4) = 90. It cannot be marked on the graph since we donโt have values that great.
Discussion 3. The Remainder Theorem states: If the polynomial P(x) is divided by x โ a, then the remainder is
__P(a)_ ___. 4. Why is this important? How this can help us graph polynomial functions?
Answers will vary. By allowing us a different way to find coordinate points on a polynomial graph we can sketch the graph more accurately.
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-4 -3 -2 -1 0 1 2 3 4
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Exercises 5โ7 (5 minutes)
Assign different groups of students one of the three problems. Have them complete their assigned problem, and then have a student from each group put their solution on the board. Having the solutions readily available allows students to start looking for a pattern without making the lesson too tedious.
5. Consider the polynomial function ๐๐(๐๐) = ๐๐๐๐๐๐ + ๐๐๐๐ โ ๐๐.
A. Divide ๐๐ by ๐๐ โ ๐๐.
B. Find ๐๐(๐๐).
f(x)x โ 2
= 3x2 + 8x โ 4
x โ 2
= (3x + 14) +24
x โ 2
f(2) = 24
6. Consider the polynomial function ๐๐(๐๐) = ๐๐๐๐ โ ๐๐๐๐๐๐ + ๐๐๐๐ + ๐๐.
A. Divide ๐๐ by ๐๐ + ๐๐. B. Find ๐๐(โ๐๐).
g(x)x + 1
=x3 โ 3x2 + 6x + 8
x + 1
= (x2 โ 4x + 10)โ2
x + 1
g(โ1) = โ2
7. Consider the polynomial function ๐๐(๐๐) = ๐๐๐๐ + ๐๐๐๐ โ ๐๐.
A. Divide ๐๐ by ๐๐ โ ๐๐. B. Find ๐๐(๐๐).
h(x)x โ 3
=x3 + 2x โ 3
x โ 3
= (x2 + 3x + 11) +30
x โ 3
h(3) = 30
Scaffolding: If students are struggling, replace the polynomials in Exercises 6 and 7 with easier polynomial functions.
Examples:
๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ2 โ 7๐ฅ๐ฅ โ 11 a. Divide by ๐ฅ๐ฅ + 1. b. Find ๐๐(โ1).
(๐ฅ๐ฅ โ 8) โ3
๐ฅ๐ฅ + 1 ๐๐(โ1) = โ3
โ(๐ฅ๐ฅ) = 2๐ฅ๐ฅ2 + 9 a. Divide by ๐ฅ๐ฅ โ 3. b. Find โ(3).
(2๐ฅ๐ฅ + 6) +27
2๐ฅ๐ฅ2 + 9 โ(3) = 27
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Discussion (7 minutes)
What is ๐๐(2)? What is ๐๐(โ1)? What is โ(3)? ๐๐(2) = 24; ๐๐(โ1) = โ2; โ(3) = 30
Looking at the results of the quotient, what pattern do we see? The remainder is the value of the function.
Stating this in more general terms, what do we suspect about the connection between the remainder from dividing a polynomial ๐๐ by ๐ฅ๐ฅ โ ๐๐ and the value of ๐๐(๐๐)? The remainder found after dividing ๐๐ by ๐ฅ๐ฅ โ ๐๐ will be the same value as ๐๐(๐๐).
Why would this be? Think about the quotient 133
. We could write this as 13 = 4 โ 3 + 1, where 4 is the quotient and 1 is the remainder.
Apply this same principle to Exercise 1. Write the following on the board, and talk through it:
๐๐(๐ฅ๐ฅ)๐ฅ๐ฅ โ 2
=3๐ฅ๐ฅ2 + 8๐ฅ๐ฅ โ 4
๐ฅ๐ฅ โ 2= (3๐ฅ๐ฅ + 14) +
24๐ฅ๐ฅ โ 2
How can we rewrite ๐๐ using the equation above? Multiply both sides of the equation by ๐ฅ๐ฅ โ 2 to get ๐๐(๐ฅ๐ฅ) = (3๐ฅ๐ฅ + 14)(๐ฅ๐ฅ โ 2) + 24.
In general we can say that if you divide polynomial ๐๐ by ๐ฅ๐ฅ โ ๐๐, then the remainder must be a number; in fact, there is a (possibly non-zero degree) polynomial function ๐๐ such that the equation,
๐๐(๐ฅ๐ฅ) = ๐๐(๐๐) โ (๐ฅ๐ฅ โ ๐๐) + ๐๐
โ โ quotient remainder
is true for all ๐ฅ๐ฅ. What is ๐๐(๐๐)?
๐๐(๐๐) = ๐๐(๐๐)(๐๐ โ ๐๐) + ๐๐ = ๐๐(๐๐) โ 0 + ๐๐ = 0 + ๐๐ = ๐๐ We have just proven the remainder theorem, which is formally stated in the box below.
Restate the remainder theorem in your own words to your partner.
While students are doing this, circulate and informally assess student understanding before asking students to share their responses as a class.
REMAINDER THEOREM: Let ๐๐ be a polynomial function in ๐ฅ๐ฅ, and let ๐๐ be any real number. Then there exists a unique polynomial function ๐๐ such that the equation
๐๐(๐ฅ๐ฅ) = ๐๐(๐ฅ๐ฅ)(๐ฅ๐ฅ โ ๐๐) + ๐๐(๐๐) is true for all ๐ฅ๐ฅ. That is, when a polynomial is divided by (๐ฅ๐ฅ โ ๐๐), the remainder is the value of the polynomial evaluated at ๐๐.
MP.8
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Exercise 8 (5 minutes)
Students may need more guidance through this exercise, but allow them to struggle with it first. After a few students have found ๐๐, share various methods used.
8. Consider the polynomial ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐๐๐ + ๐๐ + ๐๐. A. Find the value of ๐๐ so that ๐๐ + ๐๐ is a factor of ๐ท๐ท.
In order for x + 1 to be a factor of P, the remainder must be zero. Hence, since x + 1 = x โ (โ1), we must have P(โ1) = 0 so that 0 = โ1 + k โ 1 +6. Then k = โ4.
B. Find the other two factors of ๐ท๐ท for the value of ๐๐ found in Part A
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ + 1)(๐ฅ๐ฅ2 โ 5๐ฅ๐ฅ + 6) = (๐ฅ๐ฅ + 1)(๐ฅ๐ฅ โ 2)(๐ฅ๐ฅ โ 3)
Discussion (7 minutes)
Remember that for any polynomial function ๐๐ and real number ๐๐, the remainder theorem says that there exists a polynomial ๐๐ so that ๐๐(๐ฅ๐ฅ) = ๐๐(๐ฅ๐ฅ)(๐ฅ๐ฅ โ ๐๐) + ๐๐(๐๐).
What does it mean if ๐๐ is a zero of a polynomial ๐๐? ๐๐(๐๐) = 0
So what does the remainder theorem say if ๐๐ is a zero of ๐๐? There is a polynomial ๐๐ so that ๐๐(๐ฅ๐ฅ) = ๐๐(๐ฅ๐ฅ)(๐ฅ๐ฅ โ ๐๐) + 0.
How does (๐ฅ๐ฅ โ ๐๐) relate to ๐๐ if ๐๐ is a zero of ๐๐? If ๐๐ is a zero of ๐๐, then (๐ฅ๐ฅ โ ๐๐) is a factor of ๐๐.
How does the graph of a polynomial function ๐ฆ๐ฆ = ๐๐(๐ฅ๐ฅ) correspond to the equation of the polynomial ๐๐? The zeros are the ๐ฅ๐ฅ-intercepts of the graph of ๐๐. If we know a zero of ๐๐, then we know a
factor of ๐๐. If we know all of the zeros of a polynomial function, and their multiplicities, do we know the
equation of the function? Not necessarily. It is possible that the equation of the function contains some factors that
cannot factor into linear terms.
Scaffolding: Challenge early finishers with this problem:
Given that ๐ฅ๐ฅ + 1 and ๐ฅ๐ฅ โ 1 are factors of ๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ4 + 2๐ฅ๐ฅ3 โ49๐ฅ๐ฅ2 โ 2๐ฅ๐ฅ + 48, write ๐๐ in factored form.
Answer: (๐ฅ๐ฅ + 1)(๐ฅ๐ฅ โ 1)(๐ฅ๐ฅ + 8)(๐ฅ๐ฅ โ 6)
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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We have just proven the factor theorem, which is a direct consequence of the remainder theorem.
Give an example of a polynomial function with zeros of multiplicity 2 at 1 and 3.
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ โ 1)2(๐ฅ๐ฅ โ 3)2 Give another example of a polynomial function with zeros of multiplicity 2 at 1 and 3.
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ โ 1)2(๐ฅ๐ฅ โ 3)2(๐ฅ๐ฅ2 + 1) or ๐ ๐ (๐ฅ๐ฅ) = 4(๐ฅ๐ฅ โ 1)2(๐ฅ๐ฅ โ 3)2 If we know the zeros of a polynomial, does the factor theorem tell us the exact formula for the
polynomial? No. But, if we know the degree of the polynomial and the leading coefficient, we can often
deduce the equation of the polynomial.
Exercise 9 (6 minutes)
Allow students a few minutes to work on the problem and then share results.
9. Consider the graph of a degree ๐๐ polynomial shown to the right, with ๐๐-intercepts โ๐๐, โ๐๐, ๐๐, ๐๐, and ๐๐.
A. Write a formula for a possible polynomial function that the graph represents using ๐๐ as the constant factor.
๐ท๐ท(๐๐) = ๐๐(๐๐ + ๐๐)(๐๐ + ๐๐)(๐๐ โ ๐๐)(๐๐ โ ๐๐)(๐๐ โ ๐๐)
B. Suppose the ๐๐-intercept is โ๐๐. Find the value of ๐๐ so that the
graph of ๐ท๐ท has ๐๐-intercept โ๐๐.
๐ท๐ท(๐๐) =๐๐๐๐๐๐
(๐๐ + ๐๐)(๐๐ + ๐๐)(๐๐ โ ๐๐)(๐๐ โ ๐๐)(๐๐ โ ๐๐)
Discussion Points What information from the graph was needed to write the equation?
The ๐ฅ๐ฅ-intercepts were needed to write the factors. Why would there be more than one polynomial function possible?
Because the factors could be multiplied by any constant and still produce a graph with the same ๐ฅ๐ฅ-intercepts.
FACTOR THEOREM: Let ๐๐ be a polynomial function in ๐ฅ๐ฅ, and let ๐๐ be any real number. If ๐๐ is a zero of ๐๐ then (๐ฅ๐ฅ โ ๐๐) is a factor of ๐๐.
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Why canโt we find the constant factor ๐๐ by just knowing the zeros of the polynomial? The zeros only determine where the graph crosses the ๐ฅ๐ฅ-axis, not how the graph is stretched
vertically. The constant factor can be used to vertically scale the graph of the polynomial function that we found to fit the depicted graph.
Lesson Summary
REMAINDER THEOREM: Let ๐๐ be a polynomial function in ๐ฅ๐ฅ, and let ๐๐ be any real number. Then there exists a unique polynomial function ๐๐ such that the equation
๐๐(๐ฅ๐ฅ) = ๐๐(๐ฅ๐ฅ)(๐ฅ๐ฅ โ ๐๐) + ๐๐(๐๐)
is true for all ๐ฅ๐ฅ. That is, when a polynomial is divided by (๐ฅ๐ฅ โ ๐๐), the remainder is the value of the polynomial evaluated at ๐๐.
FACTOR THEOREM: Let ๐๐ be a polynomial function in ๐ฅ๐ฅ, and let ๐๐ be any real number. If ๐๐ is a zero of ๐๐, then (๐ฅ๐ฅ โ ๐๐) is a factor of ๐๐.
Example: If ๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ3 โ 5๐ฅ๐ฅ2 + 3๐ฅ๐ฅ + 9, then ๐๐(3) = 27 โ 45 + 9 + 9 = 0, so (๐ฅ๐ฅ โ 3) is a factor of ๐๐.
Closing (2 minutes)
Have students summarize the results of the remainder theorem and the factor theorem. What is the connection between the remainder when a polynomial ๐๐ is divided by ๐ฅ๐ฅ โ ๐๐ and the
value of ๐๐(๐๐)? They are the same.
If ๐ฅ๐ฅ โ ๐๐ is factor, then _________. The number ๐๐ is a zero of ๐๐.
If ๐๐(๐๐) = 0, then ____________. (๐ฅ๐ฅ โ ๐๐) is a factor of ๐๐.
Exit Ticket (5 minutes)
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Name Date
Lesson 21: The Remainder Theorem
Exit Ticket
Consider the polynomial ๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ3 + ๐ฅ๐ฅ2 โ 10๐ฅ๐ฅ โ 10.
1. Is ๐ฅ๐ฅ + 1 one of the factors of ๐๐? Explain.
2. The graph shown has ๐ฅ๐ฅ-intercepts at โ10, โ1, and โโ10. Could this be the graph of ๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ3 + ๐ฅ๐ฅ2 โ 10๐ฅ๐ฅ โ 10? Explain how you know.
Lesson 21: The Remainder Theorem
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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Exit Ticket Sample Solutions
Consider polynomial ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐ โ ๐๐๐๐๐๐ โ ๐๐๐๐.
1. Is ๐๐ + ๐๐ one of the factors of ๐ท๐ท? Explain.
๐ท๐ท(โ๐๐) = (โ๐๐)๐๐ + (โ๐๐)๐๐ โ ๐๐๐๐(โ๐๐) โ ๐๐๐๐ = โ๐๐+ ๐๐ + ๐๐๐๐ โ ๐๐๐๐ = ๐๐
Yes, ๐๐ + ๐๐ is a factor of ๐ท๐ท because ๐ท๐ท(โ๐๐) = ๐๐. Or, using factoring by grouping, we have
๐ท๐ท(๐๐) = ๐๐๐๐(๐๐ + ๐๐) โ ๐๐๐๐(๐๐ + ๐๐) = (๐๐ + ๐๐)(๐๐๐๐ โ ๐๐๐๐).
2. The graph shown has ๐๐-intercepts at โ๐๐๐๐, โ๐๐, and โโ๐๐๐๐. Could this be the graph of ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐ โ๐๐๐๐๐๐ โ ๐๐๐๐? Explain how you know.
Yes, this could be the graph of ๐ท๐ท. Since this graph has ๐๐-intercepts at โ๐๐๐๐, โ๐๐, and โโ๐๐๐๐, the factor theorem says that (๐๐ โ โ๐๐๐๐), (๐๐ โ ๐๐), and (๐๐ +โ๐๐๐๐ ) are all factors of the equation that goes with this graph. Since ๏ฟฝ๐๐ โ โ๐๐๐๐๏ฟฝ๏ฟฝ๐๐ + โ๐๐๐๐๏ฟฝ(๐๐ โ ๐๐) = ๐๐๐๐ + ๐๐๐๐ โ ๐๐๐๐๐๐ โ ๐๐๐๐, the graph shown is quite likely to be the graph of ๐ท๐ท.
Homework Problem Set Sample Solutions
1. Use the remainder theorem to find the remainder for each of the following divisions.
a. ๏ฟฝ๐๐๐๐+๐๐๐๐+๐๐๏ฟฝ
(๐๐+๐๐) b. ๐๐๐๐โ๐๐๐๐๐๐โ๐๐๐๐+๐๐
(๐๐โ๐๐)
โ๐๐ โ๐๐๐๐
c. ๐๐๐๐๐๐๐๐+๐๐๐๐๐๐๐๐โ๐๐๐๐๐๐๐๐+๐๐๐๐+๐๐
(๐๐+๐๐)
โ๐๐
d. ๐๐๐๐๐๐๐๐+๐๐๐๐๐๐๐๐โ๐๐๐๐๐๐๐๐+๐๐๐๐+๐๐
(๐๐๐๐โ๐๐)
Hint for part (d): Can you rewrite the division expression so that the divisor is in the form (๐๐ โ ๐๐) for some constant ๐๐?
๐๐
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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2. Consider the polynomial ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐๐๐ โ ๐๐. Find ๐ท๐ท(๐๐) in two ways.
๐๐(4) = 43 + 6(4)2 โ 8(4) โ 1 = 127
๐ฅ๐ฅ3+6๐ฅ๐ฅ2โ8๐ฅ๐ฅโ1
๐ฅ๐ฅโ4 has a remainder of 127, so ๐๐(4) = 127.
3. Consider the polynomial function ๐ท๐ท(๐๐) = ๐๐๐๐๐๐ + ๐๐๐๐๐๐ + ๐๐๐๐. a. Divide ๐ท๐ท by ๐๐ + ๐๐, and rewrite ๐ท๐ท in the form (divisor)(quotient)+remainder.
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ + 2)(2๐ฅ๐ฅ3 โ 4๐ฅ๐ฅ2 + 11๐ฅ๐ฅ โ 22) + 56 b. Find ๐ท๐ท(โ๐๐).
๐๐(โ2) = (โ2 + 2)๏ฟฝ๐๐(โ2)๏ฟฝ + 56 = 56
4. Consider the polynomial function ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐. a. Divide ๐ท๐ท by ๐๐ โ ๐๐, and rewrite ๐ท๐ท in the form (divisor)(quotient) + remainder.
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ โ 4)(๐ฅ๐ฅ2 + 4๐ฅ๐ฅ + 16) + 106
b. Find ๐ท๐ท(๐๐).
๐๐(4) = (4 โ 4)๏ฟฝ๐๐(4)๏ฟฝ + 106 = 106
5. Explain why for a polynomial function ๐ท๐ท, ๐ท๐ท(๐๐) is equal to the remainder of the quotient of ๐ท๐ท
and ๐๐ โ ๐๐.
The polynomial P can be rewritten in the form P(x) = (x โ a)(q(x)) + r, where q(x) is the quotient function and r is the remainder. Then P(a) = (a โ a)๏ฟฝq(a)๏ฟฝ + r. Therefore, P(a) = r.
6. Is ๐๐ โ ๐๐ a factor of the function ๐๐(๐๐) = ๐๐๐๐ + ๐๐๐๐ โ ๐๐๐๐๐๐ โ ๐๐๐๐? Show work supporting your answer.
Yes, because f(5) = 0 means that dividing by x โ 5 leaves a remainder of 0.
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7. Is ๐๐ + ๐๐ a factor of the function ๐๐(๐๐) = ๐๐๐๐๐๐ โ ๐๐๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐ + ๐๐๐๐? Show work supporting your answer.
No, because f(โ1) = โ1 means that dividing by x + 1 has a remainder of โ1.
8. A polynomial function ๐๐ has zeros of ๐๐, ๐๐, โ๐๐, โ๐๐, โ๐๐, and ๐๐. Find a possible formula for ๐ท๐ท,
and state its degree. Why is the degree of the polynomial not ๐๐?
One solution is P(x) = (x โ 2)2(x + 3)3(x โ 4). The degree of P is 6. This is not a degree 3 polynomial function because the factor (x โ 2) appears twice, and the factor (x + 3) appears 3 times, while the factor (x โ 4) appears once.
9. Consider the polynomial function ๐ท๐ท(๐๐) = ๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐๐๐๐๐. a. Verify that ๐ท๐ท(๐๐) = ๐๐. Since ๐ท๐ท(๐๐) = ๐๐, what must one of
the factors of ๐ท๐ท be?
๐๐(0) = 903 + 2(02)โ 15(0)0 = 0; ๐ฅ๐ฅ โ 0 or x.
b. Find the remaining two factors of ๐ท๐ท.
๐ท๐ท(๐๐) = ๐๐(๐๐ โ ๐๐)(๐๐ + ๐๐)
c. State the zeros of ๐ท๐ท.
๐๐ = ๐๐, ๐๐, โ๐๐
d. Sketch the graph of ๐ท๐ท.
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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10. Consider the polynomial function ๐ท๐ท(๐๐) = ๐๐๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐๐๐ โ ๐๐. a. Verify that ๐ท๐ท(โ๐๐) = ๐๐. Since ๐ท๐ท(โ๐๐) = ๐๐, what must one of the factors of ๐ท๐ท be?
๐๐(โ1) = 2(โ1)3 + 3(โ1)2 โ 2(โ1)โ 3 = 0; ๐ฅ๐ฅ + 1
b. Find the remaining two factors of ๐ท๐ท.
๐๐(๐ฅ๐ฅ) = (๐ฅ๐ฅ + 1)(๐ฅ๐ฅ โ 1)(2๐ฅ๐ฅ + 3)
c. State the zeros of ๐ท๐ท.
๐ฅ๐ฅ = โ1, 1, โ32
d. Sketch the graph of ๐ท๐ท.
11. The graph to the right is of a third-degree polynomial
function ๐๐. a. State the zeros of ๐๐.
๐ฅ๐ฅ = โ10, โ 1, 2
b. Write a formula for ๐๐ in factored form using ๐๐ for the
constant factor.
๐๐(๐ฅ๐ฅ) = ๐๐(๐ฅ๐ฅ + 10)(๐ฅ๐ฅ + 1)(๐ฅ๐ฅ โ 2)
c. Use the fact that ๐๐(โ๐๐) = โ๐๐๐๐ to find the constant factor ๐๐.
โ54 = ๐๐(โ4 + 10)(โ4 + 1)(โ4โ 2)
๐๐ = โ12
๐๐(๐ฅ๐ฅ) = โ12
(๐ฅ๐ฅ + 10)(๐ฅ๐ฅ + 1)(๐ฅ๐ฅ โ 2)
d. Verify your equation by using the fact that ๐๐(๐๐) = ๐๐๐๐.
๐๐(1) = โ12
(1 + 10)(1 + 1)(1 โ 2) = โ12
(11)(2)(โ1) = 11
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Hart Interactive โ Algebra 2 M1 Lesson 21 ALGEBRA II
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12. Find the value of ๐๐ so that ๐๐๐๐โ๐๐๐๐๐๐+๐๐๐๐โ๐๐
has remainder ๐๐.
๐๐ = โ5
13. Find the value ๐๐ so that ๐๐๐๐๐๐+๐๐โ๐๐๐๐+๐๐
has remainder ๐๐๐๐.
๐๐ = โ2
14. Show that ๐๐๐๐๐๐ โ ๐๐๐๐๐๐ + ๐๐๐๐ is divisible by ๐๐ โ ๐๐.
Let ๐๐(๐ฅ๐ฅ) = ๐ฅ๐ฅ51 โ 21๐ฅ๐ฅ + 20.
Then ๐๐(1) = 151 โ 21(1) + 20 = 1 โ 21 + 20 = 0.
Since ๐๐(1) = 0, the remainder of the quotient (๐ฅ๐ฅ51 โ 21๐ฅ๐ฅ + 20) รท (๐ฅ๐ฅ โ 1) is 0.
Therefore, ๐ฅ๐ฅ51 โ 21๐ฅ๐ฅ + 20 is divisible by ๐ฅ๐ฅ โ 1.
15. Show that ๐๐ + ๐๐ is a factor of ๐๐๐๐๐๐๐๐๐๐ + ๐๐๐๐๐๐ โ ๐๐.
Let ๐๐(๐ฅ๐ฅ) = 19๐ฅ๐ฅ42 + 18๐ฅ๐ฅ โ 1.
Then ๐๐(โ1) = 19(โ1)42 + 18(โ1)โ 1 = 19 โ 18 โ 1 = 0.
Since ๐๐(โ1) = 0, ๐ฅ๐ฅ + 1 must be a factor of ๐๐.
Lesson 21: The Remainder Theorem
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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.