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How to Simplify a Subtraction Expression

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  • 0:01 A Subtraction Expression
  • 0:56 Simplifying
  • 2:12 Example 1
  • 2:41 Example 2
  • 3:36 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After watching this video lesson, you will be able to simplify any subtraction expression by combining like terms. Learn what to look for and how easy this is to do.

A Subtraction Expression

In this video lesson, we look at subtraction expressions. These are the mathematical expressions with subtraction in them. Specifically, we will look at the subtraction expressions that have terms made up of the product of a number and a letter or variable. This means that we will look at expressions such as 5x - 3x. It might help you to visualize this problem by looking at the variable as a thing instead of a letter. For example, the x could stand for a basketball. If this is the case, then 5x means you have five basketballs and 3x means you have three basketballs. You see the subtraction sign telling you to take away three basketballs from the group of five. How many basketballs are left? Two basketballs; using the x again, we have 2x.

Simplifying

A subtraction expression can have more than one variable in it. For example, we could have an expression such as 5x - 3x - 8y. In this case, we simply combine the terms that have the same variable. So, we combine the 5x and the 3x. Since there is only one term with the y, we keep it as is. In math, we call this process simplifying. We get 2x - 8y. We can also visualize problems such as these by picturing different things for different letters. For example, in our problem 5x - 3x - 8y, we can picture motorcycles for the x and cars for y. Because motorcycles and cars are different, we can't combine them into one big group of like items. Motorcycles and cars are not alike. We can combine the two groups of motorcycles that we have, the 5x and the 3x. We see subtraction going on, so when we combine these two groups, we are actually subtracting the 3x from the 5x. We get 2x - 8y as our simplified expression.

Let's look at a couple of examples to help us understand this process even more.

Example 1

Simplify: 7x - 4x - 9.

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