The topic of simplifying expressions which contain parentheses is really part of studying the Order of Operations, but simplifying with parentheses is probably the one part of the Order of Operations that causes students the most difficulty. This lesson is meant to provide a little extra help in this area.
When you need to simplify an expression that contains parenthetical expressions (that is, that contains stuff inside parentheses), you will need to apply the Distributive Property. This is because you will be "distributing [something] over" (that is, multiplying [something] through) something else that is inside a set of parentheses; this will be a necessary step in simplifying the given expression.
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I will walk you through some examples of increasing difficulty, and you should note, as this lesson progresses, the importance of "simplifying as you go" and of doing each step neatly, completely, and exactly.
To "simplify" this, I have to get rid of the parentheses. The Distributive Property says to multiply the 3 onto everything inside the parentheses. I sometimes draw arrows to emphasize this by drawing little arrows from the multiplier out front, on to each term inside the parenthetical, like so:
Then I multiply the 3 onto the x and onto the 4:
3(x) + 3(4)
3x + 12
These two terms are "unlike", so they cannot be combined. That means that this is as far as I can go. My answer is:
3x + 12
Written all in one line, the above would look like the below:
(I would not recommend trying to work sideways like the above. Line-by-line usually has a greater chance of success.)
The error most commonly made at this stage is to take the 3 through the parentheses, but only onto the x, forgetting to carry it through onto the 4 as well. If you need to draw little arrows to help you remember to carry the multiplier through onto everything inside the parentheses, then draw them!
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I have to take the –2 through the parentheses. This gives me:
–2(x – 4)
–2(x) – 2(–4)
–2x + 8
These are two unlike terms, so I can't simplify any further. My final answer is:
–2x + 8
The common mistake students make with this type of problem is to lose a "minus" sign somewhere. For example, a student might do the following:
This is wrong!
–2(x – 4)
= –2(x) – 2(4)
= –2x – 8
The above is wrong!
Did you notice how the "–4" originally inside the parenthetical somehow turned into a plain old "4" when the –2 went through the parentheses? That's why the answer in the gray box above ended up being wrong. (Compare with the correct answer, –2x + 8.) Be careful with the "minus" signs! Until you are confident in your skills, take the time to write out the distribution, complete with the signs, as I did.
Another way to keep track of what's going on is to write out the multiplications explicitly. Below, I've used color, where the "–2" is in red, the "– 4" is in blue, the variable "x" is left as black text, and the "8" in the answer is in purple:
–2 (x – 4)
–2 (x) –2 (–4)
–2x + 8
If you have difficulty with the subtraction, then try converting it into the addition of a negative:
–2 (x – 4)
–2 (x + [–4])
–2 (x) + (–2)(–4)
–2x + 8
Do as many steps as you need to do, in order to consistently get the correct answer. Whatever works for you is "the right way" to do these!
I have to take the "minus" through the parentheses. Many students find it helpful to write in the little "understood 1" in front of the parentheses:
–1(x – 3)
Now I can clearly see that I need to take a –1 through the parentheses. From the beginning, this gives me:
–(x – 3)
–1(x – 3)
–1(x) – 1(–3)
–1x + 3
–x + 3
I have simplified as much as I can, and I have written the expression with its terms in descending order, so I'm done.
–x + 3
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Take note that the expressions "–1x + 3" and "–x + 3" are technically the same thing; in my classes, either would be perfectly acceptable as your hand-in answer. However, some teachers will accept only "–x + 3" and would count "–1x + 3" as not fully simplified. It would be wise to check with your instructor, especially if you find it helpful to write in that understood "1".
The order of operations tells me that multiplication comes before addition. I can't do the "2 +" part until I have taken the 4 through the parentheses. In other words, I have to simplify the parenthetical, so I know what I'm adding the two to, before I can actually do that addition. First, I'll take the 4 onto each of the two terms inside the parenthetical:
2 + 4(x – 1)
2 + 4(x) + 4(–1)
2 + 4x + (–4)
Now I'll move the third term, which is just a constant, next to the 2, so I can combine these "like" terms:
2 – 4 + 4x
–2 + 4x
This answer is mathematically correct, but most graders and instructors prefer that answers have their terms in "descending" order, so I'll swap the two terms to put the variable-containing term in front:
4x – 2
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If I were your instructor, I would accept either of "4x – 2" and "–2 + 4x" as a valid answer. However, most texts expect the answer to be written with its terms in descending order (which, in this case, means with the variable term first, followed by the plain number). You should know that the two expressions of the answer are mathematically exactly the same, while keeping in mind that some instructors insist that the answer be written in descending order for that answer to be considered to be completely "correct". It would probably be best to get in the habit now of writing your answers in descending order.
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