Algebra 1 (Eureka Math/EngageNY)
Course: Algebra 1 (Eureka Math/EngageNY) > Unit 4Lesson 3: Topic A: Lessons 1-2: Factoring binomials intro
- Difference of squares intro
- Factoring quadratics: Difference of squares
- Difference of squares intro
- Perfect square factorization intro
- Factoring quadratics: Perfect squares
- Perfect squares intro
- Factoring quadratics as (x+a)(x+b)
- Factoring quadratics: leading coefficient = 1
- Factoring quadratics as (x+a)(x+b) (example 2)
- More examples of factoring quadratics as (x+a)(x+b)
- Warmup: factoring quadratics intro
- Factoring quadratics intro
Factoring quadratics: Difference of squares
Learn how to factor quadratics that have the "difference of squares" form. For example, write x²-16 as (x+4)(x-4).
Factoring a polynomial involves writing it as a product of two or more polynomials. It reverses the process of polynomial multiplication.
In this article, we'll learn how to use the difference of squares pattern to factor certain polynomials. If you don't know the difference of squares pattern, please check out our video before proceeding.
Intro: Difference of squares pattern
Every polynomial that is a difference of squares can be factored by applying the following formula:
Note that and in the pattern can be any algebraic expression. For example, for and , we get the following:
The polynomial is now expressed in factored form, . We can expand the right-hand side of this equation to justify the factorization:
Now that we understand the pattern, let's use it to factor a few more polynomials.
Example 1: Factoring
Both and are perfect squares, since and . In other words:
Since the two squares are being subtracted, we can see that this polynomial represents a difference of squares. We can use the difference of squares pattern to factor this expression:
In our case, and . Therefore, our polynomial factors as follows:
We can check our work by ensuring the product of these two factors is .
Check your understanding
1) Factor .
2) Factor .
3) Can we use the difference of squares pattern to factor ?
Example 2: Factoring
The leading coefficient does not have to equal to in order to use the difference of squares pattern. In fact, the difference of squares pattern can be used here!
This is because and are perfect squares, since and . We can use this information to factor the polynomial using the difference of squares pattern:
A quick multiplication check verifies our answer.
Check your understanding
4) Factor .
5) Factor .
6) Factor .
7*) Factor .
8*) Factor .
Want to join the conversation?
- If the question is x^2 + 25 its not factorable? Why?(5 votes)
- The difference of squares: (a+b)(a-b). x^2 + 25 is not factorable since you're adding 25, not subtracting. A positive multiplied by a negative is always a negative. If you were to factor it, you would have to use imaginary numbers such as i5. The factors of 25 are 5 and 5 besides 1 and itself. Since the formula: (a-b)(a+b), it uses a positive and negative sign, making the last term always a negative.(18 votes)
- i really don't understand factoring AT ALL even after watching the videos so can someone help me because i really suck at math! thank you in advance!(6 votes)
- Are you talking about just this video (difference of squares) or about any factoring at all? If it is factoring in general, you have to go through a sequence of factoring to support your learning. So just reaching out says that you are not as bad as you think. If you say all factoring, then we will start with a=1 and go one step at a time.(12 votes)
- Does the order of the signs matter? I have gotten it right when I do (x+y)(x-y). If I did it (x-y)(x+y) would it be wrong?(5 votes)
- While it is the same answer, sometimes questions ask for a specific order.(3 votes)
- in the video how did he know what number to divide by ?(4 votes)
- I think he looked for their square roots. Like when he had 25 5*5 = 25 so that's how he figured it out. Unless that's not what you're talking about then I feel embarrassed(4 votes)
- What's the purpose of converting it to this form?(2 votes)
- It gives us the solutions to the quadratic directly! If I give you 4x^2 - 9 = 0, you can't really see the solutions. But, if I give you (2x-3)(2x+3) = 0 (which is the factored form), you can easily see that either 2x-3 = 0 or 2x+3 = 0. So, x can be 3/2 or -3/2. So, this form is important to figure the solutions to the quadratic, which would be important in the future lessons.
Another advantage to this form is in limits. Sometimes, a limit of a function can be indeterminate until you factor polynomials like this, which can cancel out terms and give us a finite limit.(7 votes)
- upvote this please(4 votes)
- yes and again no(2 votes)
- So when you have 25x-4 you have to make the 4 into a 2(2 votes)
- Yes, because the square root of 4 is 2. You should also notice the 25x^2. The square root of 25x^2 is 5x.(2 votes)
- How would you factor a "difference of squares" problem WITHOUT using this formula?
What fundamental steps or rules would you follow to do the expanding brackets steps in reverse?
= x^2 − 4
= x^2 −2x +2x −4 #This step does not seem intuitive.
Can you instead factor it by doing something with square roots?(1 vote)
- Your work above is correct. Maybe this will make your 1st step more intuitive. When you multiply 2 binomials, you usually get a trinomial (3 terms). With the difference of two squares, we get only a binomial (2 terms). Why does the middle term not exist? It's because it has a coefficient of 0. So, if you forget the pattern, stub in the middle term:
x^2 + 0x - 4
Then factor as usual. You need factors of -4 that add to 0, which leads you to the -2 and +2.
Hope this helps.(3 votes)
- how do you explain difference of squares to someone in words(2 votes)
- i cannot do this at all(2 votes)
- Do you know your perfect squares? The basis of this video is that if you have a^2-b^2, it factors to (a+b)(a-b). This works because the middle terms, -ab+ab=0.(1 vote)