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There are many ways to write the same mathematical idea. Some forms are more complex than others, but in general, simpler expressions express ideas more efficiently and are easier to evaluate. This lesson will show how to write an expression as simply as possible.
Catch-Up and Review
Here are a few recommended readings before getting started with this lesson.
Explore
How Can These Terms Be Grouped?
The applet shows some terms in a table. Try to group the terms in the table correctly.
What do these terms have in common? What happens if the terms in the same column are added or subtracted?
Discussion
Like Terms
Two or more terms in an algebraic expression are like terms if they have the same variable(s) with the same exponent(s).
Note that all constants are like terms. Like terms in an expression can be combined by using addition or subtraction to rewrite the expression in simplest form.
7xy+2x−3xy−2x2+x+5x2
In this expression, there are three sets of like terms — namely, xy-terms, x-terms, and x2-terms. Pop Quiz
Identifying Like Terms
Determine whether the terms are like terms.
Discussion
Reducing the Number of Terms
Once like terms are identified, it is possible to combine them using addition or subtraction.
Method
Combining Like Terms
In an expression, groups of like terms can be combined to write an equivalent expression with the least possible number of terms. As an example, consider the following expression.
7xy+2x−3xy−2x2+x+5x2
There are three steps to follow to combine like terms.
1
Identify Like Terms
expand_more 
2
Grouping Like Terms
expand_more Now that the like terms are identified, use the Commutative Property of Addition to rearrange the expression so that the like terms are grouped together.
3
Add and Subtract the Coefficients
expand_more Finally, combine the like terms by adding or subtracting the coefficients of the variables as well as adding or subtracting the constants.
Now that all like terms have been combined, the initial expression has been reduced to its simplest form.
7xy+2x−3xy−2x2+x+5x2⇕4xy+3x+3x2
Example
Heichi's Path to the Museum
Heichi got a part-time summer job at a local history museum. He asked his sister for directions from home to the museum. She drew a map for him. She also knows that Heichi is studying algebraic expressions, so she used algebraic expressions to show the relevant distances.
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Hint
Solution
Heichi is trying to determine the overall distance from his house to the museum along the route his sister marked for him. The route is broken into three separate sections. Each section has a unique length represented by a unique algebraic expression.
| Section | Expression |
|---|---|
| First Leg | x |
| Second Leg | 3x+7 |
| Third Leg | 4x−6 |
x+3x+7+4x−6
Notice that there are two different terms — x-terms and constant terms. These are the like terms.
x+3x+7+4x − 6
Now that the like terms have been identified, they can be combined. Use the Commutative Property of Addition to group the like terms together, then add or subtract them.
x+3x+7+4x − 6
CommutativePropAdd
Commutative Property of Addition
x+3x+4x+7 − 6
AddTerms
Add terms
8x+7−6
SubTerm
Subtract term
8x+1
Example
Weekend Visitors to the Museum
On weekends, the museum has special admission prices before noon.
Children pay x dollars and adults pay x2 dollars before noon. After noon, the prices go up to y and y2 dollars for children and adults, respectively. Heichi kept track of the number of visitors on both Saturday and Sunday in separate tables. The following table shows the number of visitors on Saturday.
| Saturday's Visitors | ||
|---|---|---|
| Children | Adults | |
| Before Noon | 7 | 12 |
| After Noon | 12 | 20 |
The table below shows the number of visitors on Sunday.
| Sunday's Visitors | ||
|---|---|---|
| Children | Adults | |
| Before Noon | 8 | 15 |
| After Noon | 3 | 4 |
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Hint
Remember that the tickets have different prices depending on the time of day.
Solution
The total amount can be written by adding the revenues from Saturday and Sunday.
The expression for Saturday's revenue can be written by adding the expressions for each part of the day.
Similar to Saturday, the expression for Sunday's revenue can be found by adding the expressions for each part of the day.
This expression represents how much money was made from admissions over the weekend.
Saturday’s Revenue+Sunday’s Revenue
The ticket revenue from Saturday can be found by multiplying the number of people that entered by the amount that they have to pay. However, since the prices change depending on the hour, this is better done in two sections. This can be written in a table. | Saturday's Visitors | |||
|---|---|---|---|
| Children ($) | Adults ($) | Total ($) | |
| Before Noon | 7x | 12x2 | 7x+12x2 |
| After Noon | 12y | 20y2 | 12y+20y2 |
Saturday’s Revenue ($)7x+12x2+12y+20y2
The same steps can be followed for Sunday's visitors. | Sunday's Visitors | |||
|---|---|---|---|
| Children ($) | Adults ($) | Total ($) | |
| Before Noon | 8x | 15x2 | 8x+15x2 |
| After Noon | 3y | 4y2 | 3y+4y2 |
Sunday’s Revenue ($)8x+15x2+3y+4y2
Now that the expressions for Saturday and Sunday are written, it is time to add them together. The like terms can be grouped by the Commutative Property of Addition to combine them easily.
7x+12x2+12y+20y2+8x+15x2+3y+4y2
CommutativePropAdd
Commutative Property of Addition
7x+8x+12y+3y+12x2+15x2+20y2+4y2
AddTerms
Add terms
15x+15y+27x2+24y2
Example
A Curious Occurrence in the Souvenir Shop
Heichi's friend Magdalena works at the souvenir shop in the museum. There are three large items that are sold in the shop.
Magdalena told Heichi that three groups of people visited the shop on Saturday.
- The first group bought three vases, four plush toys, and five paintings.
- The second group bought six plush toys, returned two vases, and bought one painting.
- The third group returned one painting and bought one vase.
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Hint
Start by writing an expression for Saturday. Then, multiply that expression by 2.
Solution
Start by writing an expression to find the amount of money made by the store on Saturday. Consider each group separately.
- The first group bought three vases, four plush toys, and five paintings.
- The second group bought six plush toys, returned two vases, and bought one painting.
- The third group returned one painting and bought one vase.
The money exchanged for each set of items is the product of the number of items sold and its corresponding price. Note that when an item is returned, the prices are negative because money is being taken from the shop and returned to the customer.
| Vases ($) | Plush Toys ($) | Paintings ($) | Total ($) | |
|---|---|---|---|---|
| First Group | 3a | 4b | 5c | 3a+4b+5c |
| Second Group | -2a | 6b | 1c | -2a+6b+1c |
| Third Group | 1a | 0 | -1c | 1a−1c |
Saturday’s Revenue ($)3a+4b+5c+6b−2a+1c−1c+1a
Magdalena mentioned that the same thing happened on Sunday. This means that the whole expression has to be multiplied by 2 to find the expression for the money made from both days. Weekend Revenue ($)2(3a+4b+5c+6b−2a+1c−1c+1a)
This expression can be simplified by combining like terms first and then distributing the 2 or by distributing first. Either process will result in the simplified expression. Here, the terms will be combined first.
2(3a+4b+5c+6b−2a+1c−1c+1a)
CommutativePropAdd
Commutative Property of Addition
2(3a−2a+1a+4b+6b+5c+1c−1c)
AddTerms
Add terms
2(4a−2a+10b+6c−1c)
SubTerms
Subtract terms
2(2a+10b+5c)
Distr
Distribute 2
2⋅2a+2⋅10b+2⋅5c
Multiply
Multiply
4a+20b+10c
Closure
Grouping Like Terms
The beginning of this lesson presented a table to group like terms.
The column headers identify the type of term. Since all constant terms are like terms, they are grouped in the first column. The terms in the other columns indicate which variables are to be placed there. 
These terms can now be combined by adding or subtracting them!
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