Intro to factors & divisibility
Learn what it means for polynomials to be factors of other polynomials or to be divisible by them.
What we need to know for this lesson
A monomial is an expression that is the product of constants and nonnegative integer powers of , like . A polynomial is an expression that consists of a sum of monomials, like .
What we will learn in this lesson
In this lesson, we will explore the relationship between factors and divisibility in polynomials and also learn how to determine if one polynomial is a factor of another.
Factors and divisibility in integers
In general, two integers that multiply to obtain a number are considered factors of that number.
For example, since , we know that and are factors of .
One number is divisible by another number if the result of the division is an integer.
For example, since and , then is divisible by and . However, since , then is not divisible by .
Notice the mutual relationship between factors and divisibility:
Since (which means is a factor of ), we know that (which means is divisible by ).
In the other direction, since (which means is divisible by ), we know that (which means is a factor of ).
This is true in general: If is a factor of , then is divisible by , and vice versa.
Factors and divisibility in polynomials
This knowledge can be applied to polynomials as well.
When two or more polynomials are multiplied, we call each of these polynomials factors of the product.
For example, we know that . This means that and are factors of .
Also, one polynomial is divisible by another polynomial if the quotient is also a polynomial.
For example, since and since , then is divisible by and . However, since , we know that is not divisible by .
With polynomials, we can note the same relationship between factors and divisibility as with integers.
In general, if for polynomials , , and , then we know the following:
- and are factors of .
- is divisible by and .
Check your understanding
1) Complete the sentence about the relationship expressed by .
, and is
2) A teacher writes the following product on the board:
Miles concludes that is a factor of .
Jude concludes that is divisible by .
Who is correct?
Determining factors and divisibility
Example 1: Is divisible by ?
To answer this question, we can find and simplify . If the result is a monomial, then is divisible by . If the result is not a monomial, then is not divisible by .
Since the result is a monomial, we know that is divisible by . (This also implies that is a factor of .)
Example 2: Is a factor of ?
If is a factor of , then is divisible by . So let's find and simplify .
Notice that the term is not a monomial since it is a quotient, not a product. Therefore we can conclude that is not a factor of .
In general, to determine whether one polynomial is divisible by another polynomial , or equivalently whether is a factor of , we can find and examine .
If the simplified form is a polynomial, then is divisible by and is a factor of .
Check your understanding
3) Is divisible by ?
4) Is a factor of ?
5*) Which of the following monomials are factors of ?
6*) The area of a rectangle with height units and base units is square units.
An area model for a rectangle that has a height of x plus one and a width of x plus four. The area of the rectangle is x squared plus five x plus four.
Which of the following are factors of ?
Why are we interested in factoring polynomials?
Just as factoring integers turned out to be very useful for a variety of applications, so is polynomial factorization!
Specifically, polynomial factorization is very useful in solving quadratic equations and simplifying rational expressions.
If you'd like to see this, check out the following articles:
The next step in the factoring process involves learning how to factor monomials. You can learn about this in our next article.
Want to join the conversation?
- what is a factor(9 votes)
- A number that multiplies to another number.(30 votes)
- The lesson was a little hard man...(17 votes)
- I'm glad I'm not the only one :/ but if we practice a lot we'll get it eventually!(7 votes)
- Hey all. Confused on last question. Wouldn’t x2+5x be a factor since you just cancel the x2+5x on top and bottom? Or is it not just because of the problem being about Area?(7 votes)
- I realize this was posted 8 months ago, but this is a common mistake so I would like to address it. x^2+5x is not a factor of this expression because it is being added to 4. If that sum were multiplied by 4 instead of added to it, then it would be a factor. The fact that the expression is a sum of x^2+5 and 4 and not a product of the two means that x^2+5 cannot be a factor of x^2+5x+4. I hope that makes sense and clears this up for anyone else wondering the same thing.(25 votes)
- This lesson was easy for me how about y`all?(8 votes)
- What's the easiest way to tell a number is a factor of another?(5 votes)
- Think about what 2 numbers multiply together to make that number. For example 3 x 4 = 12 therefore 3 and 4 are factors.(5 votes)
- i really don't understand this topic how do you do this(5 votes)
- An integer can only be a factor of another integer if it is a monomial?(3 votes)
- Does the factor of a polynomial always have to be a monomial?
e.g. 3(3x^2 + 3x + 3)
factors would be 3 and (3x^2 + 3x + 3)?(2 votes)
- A polynomial can have a monorail factor if it's terms have a common factor.But it can also have binomial and trionomial factors that can't be factored further.For example: x^3-1=(x-1)(x^2+x+1)
3(3x^2+3x+3)=9(x^2+x+1) So, the factors are 9 and (x^2+x+1).(1 vote)
- Maybe this is supposed to be obvious, but when you look at a problem, how do you know if you're supposed to factor or distribute? Am I the only one that is very confused about this?(2 votes)
- I am not sure this completely applies to this particular video. Anyway, these are sort of opposite operations, so it all depends on what you see. If you have parentheses, that will be the indication that distributing may be important 3(x-5). If you do not have parentheses, then factoring may be importnat such as 3x^2 + 15x.(1 vote)
- do we to multiple the withs?(2 votes)
- There should only be one width, but you do multiply length times width to get the area.(0 votes)