12.5: Division of Polynomials
What if you had a polynomial like and you wanted to divide it by a monomial like or a binomial like ? How would you do so? After completing this Concept, you'll be able to divide polynomials like this one by monomials and binomials.
Try This
To check your answers to long division problems involving polynomials, try the solver at http://calc101.com/webMathematica/long-divide.jsp . It shows the long division steps so you can tell where you may have made a mistake.
Watch This
CK-12 Foundation: 1205S Division of Polynomials
Guidance
A rational expression is formed by taking the quotient of two polynomials.
Some examples of rational expressions are
Just as with rational numbers, the expression on the top is called the numerator and the expression on the bottom is called the denominator . In special cases we can simplify a rational expression by dividing the numerator by the denominator.
Divide a Polynomial by a Monomial
We’ll start by dividing a polynomial by a monomial. To do this, we divide each term of the polynomial by the monomial. When the numerator has more than one term, the monomial on the bottom of the fraction serves as the common denominator to all the terms in the numerator.
Example A
Divide.
a)
b)
c)
Solution
a)
b)
c)
A common error is to cancel the denominator with just one term in the numerator.
Consider the quotient .
Remember that the denominator of 4 is common to both the terms in the numerator. In other words we are dividing both of the terms in the numerator by the number 4.
The correct way to simplify is:
A common mistake is to cross out the number 4 from the numerator and the denominator, leaving just . This is incorrect, because the entire numerator needs to be divided by 4.
Example B
Divide .
Solution
The negative sign in the denominator changes all the signs of the fractions:
Divide a Polynomial by a Binomial
We divide polynomials using a method that’s a lot like long division with numbers. We’ll explain the method by doing an example.
Example C
Divide .
Solution
When we perform division, the expression in the numerator is called the dividend and the expression in the denominator is called the divisor .
To start the division we rewrite the problem in the following form:
We start by dividing the first term in the dividend by the first term in the divisor: .
We place the answer on the line above the term:
Next, we multiply the term in the answer by the divisor, , and place the result under the dividend, matching like terms. times is , so we put that under the divisor:
Now we subtract from . It is useful to change the signs of the terms of to and add like terms vertically:
Now, we bring down the 5, the next term in the dividend.
And now we go through that procedure once more. First we divide the first term of by the first term of the divisor. divided by is 1, so we place this answer on the line above the constant term of the dividend:
Multiply 1 by the divisor, , and write the answer below , matching like terms.
Subtract from by changing the signs of to and adding like terms:
Since there are no more terms from the dividend to bring down, we are done. The quotient is and the remainder is 2.
Remember that for a division with a remainder the answer is . So the answer to this division problem is .
Check
To check the answer to a long division problem we use the fact that
For the problem above, here’s how we apply that fact to check our solution:
The answer checks out.
Watch this video for help with the Examples above.
CK-12 Foundation: Division of Polynomials
Vocabulary
- A rational expression is formed by taking the quotient of two polynomials.
Guided Practice
Divide .
Solution
When we perform division, the expression in the numerator is called the dividend and the expression in the denominator is called the divisor .
To start the division we rewrite the problem in the following form:
We start by dividing the first term in the dividend by the first term in the divisor: .
We place the answer on the line above the term:
Next, we multiply the term in the answer by the divisor, , and place the result under the dividend, matching like terms. times is , so we put that under the divisor:
Now we subtract from . It is useful to change the signs of the terms of to and add like terms vertically:
Now, we bring down the 17, the next term in the dividend.
And now we go through that procedure once more. First we divide the first term of by the first term of the divisor. divided by is 4, so we place this answer on the line above the constant term of the dividend:
Multiply 4 by the divisor, , and write the answer below , matching like terms.
Subtract from by changing the signs of to and adding like terms:
Since there are no more terms from the dividend to bring down, we are done. The quotient is and the remainder is 1.
Remember that for a division with a remainder the answer is . So the answer to this division problem is .
Check
To check the answer to a long division problem we use the fact that
For the problem above, here’s how we apply that fact to check our solution:
The answer checks out.
Practice
Divide the following polynomials:
Image Attributions
Description
Learning Objectives
Here you'll learn how to divide polynomials by monomials and binomials.