Factoring Simple Expressions

Introduction

Factoring Simple Expressions is about rewriting an algebraic expression as a product of simpler factors. For example, $12 x + 18$ can be rewritten as $6 (2 x + 3)$ . The two forms are equivalent because they have the same value for every allowed value of $x$ .

Factoring is the reverse of using the distributive property. It helps you see structure in an expression, simplify later algebra, solve problems with areas, and prepare for more advanced factorization.

In this aiMOOC you will learn how to identify common factors, find the greatest common factor, factor simple expressions, and check your result by expanding.

Datei:Factor tree of 24.png

A factor tree reminds you that whole numbers can be broken into factors. That same idea helps when you factor the numerical coefficients in algebraic terms.

Learning Goals

By the end of this course, you should be able to explain what a factor is, identify the greatest common factor of two or more terms, rewrite a sum or difference as a product, include common variable factors when appropriate, and verify a factored expression by expanding it.

You should already be comfortable with whole-number arithmetic, multiplication, division, variables, terms, and the basic distributive property.

Core Ideas

Factors, Terms, and Coefficients

A factor is a number or expression multiplied by another number or expression. In $5 x$ , both $5$ and $x$ are factors.

A term is a part of an expression separated by addition or subtraction signs. In $8 x + 12$ , the terms are $8 x$ and $12$ .

A coefficient is the numerical factor multiplying a variable. In $8 x$ , the coefficient is $8$ .

When you factor an expression, you look for something that is a factor of every term.

Algebra tiles can represent constants, variables, and squared variables. Physical or paper tiles can make the structure of an expression visible before you write the symbolic factorization.

The Greatest Common Factor

The greatest common factor, often called the GCF, is the greatest factor shared by all relevant numbers or terms.

For $12 x + 18$ , the numerical coefficients are $12$ and $18$ . Their greatest common factor is $6$ . Therefore:

$12 x + 18 = 6 (2 x + 3)$

For $10 x + 15 x^{2}$ , both terms contain a factor of $5 x$ . Therefore:

$10 x + 15 x^{2} = 5 x (2 + 3 x)$

For Grades 7–8, it is useful to separate the process into two questions: What number divides every coefficient? and What variable factor appears in every term?

Factoring Reverses the Distributive Property

The distributive property says:

$a (b + c) = a b + a c$

Factoring uses the same relationship in reverse:

$a b + a c = a (b + c)$

For example:

$4 x + 20 = 4 (x + 5)$

The common factor $4$ is placed outside the parentheses. Inside the parentheses, you write what remains after dividing each original term by $4$ .

The rectangle model shows why distribution and factoring are linked: one large area can be viewed as the sum of smaller areas, or the sum can be recombined into a product of side lengths.

Factoring Step by Step

Method for Simple Expressions

Use this routine when all terms share a common factor.

Identify terms: Separate the expression into terms using addition and subtraction signs.
Find the GCF: Find the greatest numerical factor common to all coefficients.
Find common variables: Include any variable factor present in every term.
Divide each term: Divide every original term by the complete common factor.
Write the product: Place the common factor outside parentheses and the quotients inside.
Check by expanding: Distribute the outside factor and confirm that you recover the original expression.

Worked Example: Numerical Common Factor

Factor $18 x + 24$ completely.

The terms are $18 x$ and $24$ . The greatest common factor of $18$ and $24$ is $6$ . Divide each term by $6$ :

$18 x \div 6 = 3 x$

$24 \div 6 = 4$

So:

$18 x + 24 = 6 (3 x + 4)$

Check by distributing:

$6 (3 x + 4) = 18 x + 24$

Because the expanded form matches the original expression, the factorization is correct.

Worked Example: Common Variable Factor

Factor $12 x^{2} + 18 x$ .

The coefficients $12$ and $18$ share a greatest common factor of $6$ . Both terms also contain at least one factor of $x$ . The complete common factor is therefore $6 x$ .

$12 x^{2} + 18 x = 6 x (2 x + 3)$

Check:

$6 x (2 x + 3) = 12 x^{2} + 18 x$

This example is especially useful in Grade 8 because it combines number factors with variable factors.

Worked Example: A Negative Term

Factor $- 8 y + 12$ .

The greatest positive common factor is $4$ , so one correct factorization is:

$- 8 y + 12 = 4 (- 2 y + 3)$

You may also factor out $- 4$ :

$- 8 y + 12 = - 4 (2 y - 3)$

Both forms are equivalent. In later algebra, factoring out a negative factor is sometimes useful because it can make the first term inside the parentheses positive.

Area Models and Visual Thinking

Factoring can describe dimensions. Imagine two adjacent rectangular strips that both have a width of $3$ metres. One strip has length $x$ metres and the other has length $4$ metres. Their combined area is:

$3 x + 12$

Factoring gives:

$3 x + 12 = 3 (x + 4)$

The factored form shows the dimensions of the whole rectangle: width $3$ and total length $x + 4$ .

This algebra-tile image shows a more advanced area-model example. You do not need to master quadratic factoring in this course, but the image gives you a preview of how the same product-and-area idea extends to later algebra.

Worked Practice

Try each expression before reading the explanation.

Expression	Common factor	Factored form	Quick check
$6 x + 9$	$3$	$3 (2 x + 3)$	$3 \cdot 2 x + 3 \cdot 3 = 6 x + 9$
$14 a - 21$	$7$	$7 (2 a - 3)$	$7 \cdot 2 a - 7 \cdot 3 = 14 a - 21$
$20 m + 30$	$10$	$10 (2 m + 3)$	$10 \cdot 2 m + 10 \cdot 3 = 20 m + 30$
$9 x^{2} + 12 x$	$3 x$	$3 x (3 x + 4)$	$3 x \cdot 3 x + 3 x \cdot 4 = 9 x^{2} + 12 x$
$16 p - 24 q$	$8$	$8 (2 p - 3 q)$	$8 \cdot 2 p - 8 \cdot 3 q = 16 p - 24 q$

Common Mistakes and Self-Check

Mistake 1: Taking a common factor that is not the greatest. For example, $12 x + 18 = 3 (4 x + 6)$ is correct, but it is not fully factored because $4 x + 6$ still has a common factor of $2$ . The fully factored form is $6 (2 x + 3)$ .

Mistake 2: Forgetting to divide every term. If you factor $5$ from $10 x + 15$ , the inside terms must be $2 x$ and $3$ .

Mistake 3: Losing a minus sign. In $14 a - 21 = 7 (2 a - 3)$ , the negative sign must remain with the second inside term.

Mistake 4: Missing a variable factor. In $12 x^{2} + 18 x$ , both terms contain $x$ , so factoring only $6$ does not produce the most complete common-factor form.

Best self-check: expand. If distribution returns the exact original expression, your factorization is equivalent.

Interactive Tasks

Quiz: Test Your Knowledge

What does it mean to factor an algebraic expression? (Rewrite it as a product) (!Rewrite it as a fraction) (!Replace every variable) (!Add all coefficients)

What is the greatest common factor of 12 and 18? (6) (!2) (!3) (!36)

Which property connects expanding and factoring? (Distributive property) (!Commutative property only) (!Identity property only) (!Zero product property only)

What is the greatest common numerical factor of 15x and 20? (5) (!10) (!15) (!20)

If every term in an expression contains x, what can be true? (x can be a common factor) (!x must equal zero) (!x must be removed) (!x becomes a coefficient)

After factoring 4 from 12x plus 20, what is the coefficient of x inside the group? (3) (!4) (!5) (!12)

Which common factor should you take first to factor 18x plus 24 completely? (6) (!2) (!3) (!9)

What is the most reliable way to check a simple factorization? (Expand the factored form) (!Change every sign) (!Square each term) (!Delete the common factor)

What is a coefficient? (A number multiplying a variable) (!A variable with no number) (!A sign between terms) (!A pair of parentheses)

What is the greatest positive common numerical factor of negative 6x and positive 9? (3) (!2) (!6) (!9)

Memory Game

Factor	A quantity multiplied by another quantity to form a product
Term	A part of an expression separated by addition or subtraction
Coefficient	The numerical factor multiplying a variable
GCF	The greatest factor shared by all selected terms
Distributive property	A rule connecting a product with a sum or difference
Equivalent expressions	Different forms that have the same value

Drag and Drop

Match the correct terms.	Topic
Greatest common factor	Largest shared factor of all terms
Common variable factor	Variable part present in every term
Reverse distribution	Rewriting a sum or difference as a product
Factored form	Expression written as multiplication of factors
Expanded form	Expression produced after distributing multiplication

Crossword Puzzle

Factor	What do you call a quantity multiplied by another quantity in a product?
Variable	What letter or symbol can represent a changing or unknown value?
Coefficient	What is the numerical factor multiplying a variable called?
Distributive	Which property name describes multiplying across a sum or difference?
Equivalent	What word describes two expressions with the same value?
Rectangle	Which shape is often used in an area model for factoring?

LearningApps

Cloze Text

Open-Ended Tasks

Easy

Factor Card Sort: Create twelve cards showing simple expanded expressions and twelve matching cards showing factored forms; mix them, match the pairs, and explain two of your choices to a partner.
GCF Interview: Interview a classmate about how they find the greatest common factor of two numbers, record their method in clear English, and compare it with your own method.
Algebra Poster: Design a one-page poster that explains factoring as reverse distribution and includes at least three correct examples and one self-check.
Distributive Property Video: Record a short video in which you expand one expression and then reverse the process to factor it again.

Standard

Algebra Tile Model: Build paper or physical algebra tiles, model a simple expression with a common factor, photograph or draw the model, and explain how the groups show the factorization.
Rectangle Area Investigation: Draw two adjacent rectangles with one shared side length, write the total area as a sum, factor the expression, and explain what the factored form says about the whole rectangle.
Error Analysis: Invent three realistic factoring mistakes, solve each one correctly, and write feedback that would help another learner understand the error.
Factoring Mini-Lesson: Prepare and teach a five-minute mini-lesson on common-factor factoring to a small group, then collect one question from your audience and answer it.

Advanced

Factoring Strategy Guide: Create a decision guide that helps a learner decide whether to factor out a number, a variable, or both, and test the guide on at least eight expressions.
School Space Modeling: Visit a classroom, corridor, sports area, or other suitable school space, create a simplified rectangle-based area model, and show how a factored expression can represent combined dimensions or repeated widths.
Expression Experiment: Use a spreadsheet or a short computer program to generate expressions with known common factors, factor them by hand, and verify the results by expanding.
Peer Teaching Project: Design a short practice session for younger learners that combines explanation, visual media, guided practice, and an exit question about factoring simple expressions.

Learning Assessment

Explain and verify: Factor $14 x + 21$ , explain why your common factor is greatest, and verify your answer by expanding.
Compare factorizations: Decide whether $2 (6 x + 9)$ and $6 (2 x + 3)$ represent the same expanded expression, then explain which form is more completely factored and why.
Diagnose an error: A learner writes $10 x + 15 = 5 (2 x + 15)$ ; identify the exact error, correct it, and show a distribution check.
Create an example: Write an expression whose complete common factor is $4 x$ , factor it, and justify why no larger common factor is possible.
Transfer to geometry: Create a two-part rectangle area problem whose total area can be represented by a simple expression, then factor the expression and interpret both factors as dimensions or shared measures.
Reason about signs: Compare factoring $- 8 y + 12$ by $4$ and by $- 4$ ; explain why both results are equivalent and when one form may be easier to use.

Evidence of Learning

Knowledge: You can define factor, term, coefficient, greatest common factor, distributive property, factored form, and expanded form.
Skills: You can identify common numerical and variable factors, factor simple sums and differences, and verify results by expansion.
Reasoning: You can explain why factoring is reverse distribution and justify why a chosen factor is the greatest common factor.
Products: You can produce correct worked examples, diagrams, card sorts, short explanations, models, or videos that communicate the factoring process.
Transfer: You can use factoring in new contexts such as rectangle-area models, error analysis, peer teaching, and generated expressions.
Communication: You can describe your method in clear mathematical English and respond to questions about each step.

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