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9.1: Addition and Subtraction of Polynomials

Difficulty Level: At Grade Created by: CK-12

So far we have discussed linear functions and exponential functions. This lesson introduces polynomial functions.

Definition: A polynomial is an expression made with constants, variables, and positive integer exponents of the variables.

An example of a polynomial is: 4x3+2x23x+1. There are four terms: 4x3, 2x2, 3x, and 1. The numbers appearing in each term in front of the variable are called the coefficients. 4, 2, and 3 are coefficients because those numbers are in front of a variable. The number appearing all by itself without a variable is called a constant. 1 is the constant because it is by itself.

Example 1: Identify the following expressions as polynomials or non-polynomials.

(a) 5x22x

(b) 3x22x2

(c) xx1

(d) 5x3+1

(e) 4x13

(f) 4xy22x2y3+y33x3

Solution:

(a) 5x22x This is a polynomial.

(b) 3x22x2 This is not a polynomial because it has a negative exponent.

(c) xx1 This is not a polynomial because is has a square root.

(d) 5x3+1 This is not a polynomial because the power of x appears in the denominator.

(e) 4x13 This is not a polynomial because it has a fractional exponent.

(f) 4xy22xy3+y33x3 This is a polynomial.

Classifying Polynomials by Degree

The degree of a polynomial is the largest exponent of a single term.

  • 4x3 has a degree of 3 and is called a cubic term or 3rd order term.
  • 2x2 has a degree of 2 and is called a quadratic term or 2nd order term.
  • 3x has a degree of 1 and is called a linear term or 1st order term.
  • 1 has a degree of 0 because there is no variable.

Polynomials can have more than one variable. Here is another example of a polynomial: t46s3t212st+4s45. This is a polynomial because all exponents on the variables are positive integers. This polynomial has five terms. Note: The degree of a term is the sum of the powers on each variable in the term.

t4 has a degree of 4, so it’s a 4th order term.

6s3t2 has a degree of 5, so it’s a 5th order term.

12st has a degree of 2, so it’s a 2nd order term.

4s4 has a degree of 4, so it’s a 4th order term.

–5 is a constant, so its degree is 0.

Since the highest degree of a term in this polynomial is 5, this is a polynomial of degree 5 or a 5th order polynomial.

Example 2: Identify the coefficient on each term, the degree of each term, and the degree of the polynomial.

x43x3y2+8x12

Solution: The coefficients of each term in order are 1, –3, 8 and the constant is –12.

The degrees of each term are 4, 5, 1, and 0. Therefore, the degree of the polynomial is 5.

A monomial is a one-termed polynomial. It can be a constant, a variable, or a combination of constants and variables. Examples of monomials are: b2; 6; 2ab2; 14x2

Rewriting Polynomials in Standard Form

Often, we arrange the terms in a polynomial in standard from in which the term with the highest degree is first and is followed by the other terms in order of decreasing power. The first term of a polynomial in this form is called the leading term, and the coefficient in this term is called the leading coefficient.

Example 3: Rearrange the terms in the following polynomials so that they are in standard form. Indicate the leading term and leading coefficient of each polynomial.

(a) 73x3+4x

(b) aba3+2b

Solution:

(a) 73x3+4x is rearranged as 3x3+4x+7. The leading term is 3x3 and the leading coefficient is –3.

(b) aba3+2b is rearranged as a3+ab+2b. The leading term is a3 and the leading coefficient is –1.

Simplifying Polynomials

A polynomial is simplified if it has no terms that are alike. Like terms are terms in the polynomial that have the same variable(s) with the same exponents, but they can have different coefficients.

2x2y and 5x2y are like terms.

6x2y and 6xy2 are not like terms.

If we have a polynomial that has like terms, we simplify by combining them.

& x^2 + \underline{6xy}-\underline{4xy} + y^2\\
& \qquad \nearrow \qquad \nwarrow\\
& \qquad \text{Like terms}

This polynomial is simplified by combining the like terms 6xy4xy=2xy. We write the simplified polynomial as x2+2xy+y2.

Example 4: Simplify by collecting and combining like terms.

a3b35ab4+2a3ba3b3+3ab4a2b

Solution: Use the Commutative Property of Addition to reorganize like terms then simplify.

& = (a^3b^3-a^3b^3) + (-5ab^4+3ab^4) + 2a^3b-a^2b\\
& = 0-2ab^4+2a^3b-a^2b\\
& = -2ab^4+2a^3 b-a^2 b

Adding and Subtracting Polynomials

To add or subtract polynomials, you have to group the like terms together and combine them to simplify.

Example 5: Add and simplify 3x24x+7 and 2x34x26x+5.

Solution: Add 3x24x+7 and 2x34x26x+5.

(3x^2-4x+7)+(2x^3-4x^2-6x+5)&=2x^3+(3x^2-4x^2 )+(-4x-6x)+(7+5)\\
&=2x^3-x^2-10x+12

Multimedia Link: For more explanation of polynomials, visit http://www.purplemath.com/modules/polydefs.htm - Purplemath’s website.

Example 6: Subtract 5b22a2 from 4a28ab9b2.

Solution:

(4a^2-8ab-9b^2)-(5b^2-2a^2)&=[(4a^2- (-2a^2)]+(-9b^2-5b^2)-8ab\\
& = 6a^2-14b^2-8ab

Solving Real-World Problems Using Addition or Subtraction of Polynomials

Polynomials are useful for finding the areas of geometric objects. In the following examples, you will see this usefulness in action.

Example 7: Write a polynomial that represents the area of each figure shown.

(a)

(b)

Solution: The blue square has area: yy=y2.

The yellow square has area: xx=x2.

The pink rectangles each have area: xy=xy.

\text{Test area} & = y^2+x^2+xy+xy\\
& = y^2 + x^2 + 2xy

To find the area of the green region we find the area of the big square and subtract the area of the little square.

The big square has area yy=y2.

The little square has area xx=x2.

Area of the green region =y2x2

Practice Set

Sample explanations for some of the practice exercises below are available by viewing the following video. Note that there is not always a match between the number of the practice exercise in the video and the number of the practice exercise listed in the following exercise set.  However, the practice exercise is the same in both.

CK-12 Basic Algebra: Addition and Subtraction of Polynomials (15:59)

Define the following key terms.

  1. Polynomial
  2. Monomial
  3. Degree
  4. Leading coefficient

For each of the following expressions, decide whether it is a polynomial. Explain your answer.

  1. x2+3x12
  2. 13x2y9y2
  3. 3x3
  4. 23t21t2

Express each polynomial in standard form. Give the degree of each polynomial.

  1. 32x
  2. 8x4x+5x2+11x410
  3. 84x+3x3
  4. 16+5f87f3
  5. 5+2x5x2+8x3
  6. x29x4+12

Add and simplify.

  1. (x+8)+(3x5)
  2. (8r46r23r+9)+(3r3+5r2+12r9)
  3. (2x2+4x12)+(7x+x2)
  4. (2a2b2a+9)+(5a2b4b+5)
  5. (6.9a22.3b2+2ab)+(3.1a2.5b2+b)

Subtract and simplify.

  1. (t+15t2)(5t2+2t9)
  2. (y2+4y5)(5y2+2y+7)
  3. (h7+2h5+13h3+4h2h1)(3h5+20h33h2+8h4)
  4. (5m2m)(3m2+4m5)
  5. (2a2b3ab2+5a2b2)(2a2b2+4a2b5b2)

Find the area of the following figures.

Mixed Review

  1. Solve by graphing {y=13x4y=4x+10.
  2. Solve for u: 12=4u.
  3. Graph y=|x4|+3 on a coordinate plane.
    1. State its domain and range.
    2. How has this graph been shifted from the parent function f(x)=|x|?
  4. Two dice are rolled. The sum of the values are recorded.
    1. Define the sample space.
    2. What is the probability the sum of the dice is nine?
  5. Consider the equation y=6500(0.8)x.
    1. Sketch the graph of this function.
    2. Is this exponential growth or decay?
    3. What is the initial value?
    4. What is its domain and range?
    5. What is the value when x=9.5?
  6. Write an equation for the line that is perpendicular to y=5 and contains the ordered pair (6, –5)

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8 , 9

Date Created:

Feb 22, 2012

Last Modified:

Dec 11, 2014
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CK.MAT.ENG.SE.1.Algebra-Basic.9.1

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