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Absolute Value

Elizabeth Stapel

Absolute Value

The concept of absolute value has many uses, but you probably won't see anything interesting for a few more classes yet.

There is a technical definition for absolute value, but you could easily never need it. For now, you should view the absolute value of a number as its distance from zero.

Let's look at the number line:

number line

The absolute value of x, denoted "| x |" (and which is read as "the absolute value of x"), is the distance of x from zero. This is why absolute value is never negative; absolute value only asks "how far?" , not "in which direction?" This means not only that | 3 | = 3, because 3 is three units to the right of zero, but also that | –3 | = 3, because –3 is three units to the left of zero.

abs(-3) = abs(3) = 3

Warning: The absolute-value notation is bars, not parentheses or brackets. Use the proper notation; the other notations do not mean the same thing.

It is important to note that the absolute value bars do NOT work in the same way as do parentheses. Whereas –(–3) = +3, this is NOT how it works for absolute value:

Simplify –| –3 |.

Given –| –3 |, I first handle the absolute value part, taking the positive and converting the absolute value bars to parentheses:

–| –3 | = –(+3)

Now I can take the negative through the parentheses:

–| –3 | = –(3) = –3

As this illustrates, if you take the negative of an absolute value, you will get a negative number for your answer.

When typing math as text, such as in an e-mail, the "pipe" character is usually used to indicate absolute values. The "pipe" is probably a shift-key somewhere north of the "Enter" key on your keyboard. While the "pipe" denoted on the physical keyboard key may look like a "broken" line, the typed character should display on your screen as a solid vertical bar. If you cannot locate a "pipe" character, you can use the "abs()" notation instead, so that "the absolute value of negative 3" would be typed as "abs(–3)".

Here are some more sample simplifications:

Simplify | –8 |.

| –8 | = 8 Copyright © Elizabeth Stapel 2000-2011 All Rights Reserved

Simplify | 0 – 6 |.

| 0 – 6 | = | –6 | = 6

Simplify | 5 – 2 |.

| 5 – 2 | = | 3 | = 3

Simplify | 2 – 5 |.

| 2 – 5 | = | –3 | = 3

Simplify | 0(–4) |.

| 0(–4) | = | 0 | = 0

Why is the absolute value of zero equal to "0"? Ask yourself: How far is zero from 0? Zero units, right? So | 0 | = 0.

Simplify | 2 + 3(–4) |.

| 2 + 3(–4) | = | 2 – 12 | = | –10 | = 10

Simplify –| –4 |.

–| –4| = –(4) = –4

Simplify –| (–2)2 |.

–| (–2)2 | = –| 4 | = –4

Simplify –| –2 |2

–| –2 |2 = –(2)2 = –(4) = –4

Simplify (–| –2 |)2.

(–| –2 |)2 = (–(2))2 = (–2)2 = 4

Sometimes you will be asked to insert an inequality sign between two absolute values, such as:

Insert the correct inequality: | –4 | _____ | –7 |

Whereas –4 > –7 (because it is further to the right on the number line than is –7), I am dealing here with the absolute values. Since:

| –4 | = 4

| –7 | = 7,

...and since 4 < 7, then the solution is:

| –4 | < | –7 |.

When the number inside the absolute value (the "argument" of the absolute value) was positive anyway, we didn't change the sign when we took the absolute value.

Absolute Value

Elizabeth Stapel

Absolute Value

The concept of absolute value has many uses, but you probably won't see anything interesting for a few more classes yet.

There is a technical definition for absolute value, but you could easily never need it. For now, you should view the absolute value of a number as its distance from zero.

Let's look at the number line:

number line

The absolute value of x, denoted "| x |" (and which is read as "the absolute value of x"), is the distance of x from zero. This is why absolute value is never negative; absolute value only asks "how far?" , not "in which direction?" This means not only that | 3 | = 3, because 3 is three units to the right of zero, but also that | –3 | = 3, because –3 is three units to the left of zero.

abs(-3) = abs(3) = 3

Warning: The absolute-value notation is bars, not parentheses or brackets. Use the proper notation; the other notations do not mean the same thing.

It is important to note that the absolute value bars do NOT work in the same way as do parentheses. Whereas –(–3) = +3, this is NOT how it works for absolute value:

Simplify –| –3 |.

Given –| –3 |, I first handle the absolute value part, taking the positive and converting the absolute value bars to parentheses:

–| –3 | = –(+3)

Now I can take the negative through the parentheses:

–| –3 | = –(3) = –3

As this illustrates, if you take the negative of an absolute value, you will get a negative number for your answer.

When typing math as text, such as in an e-mail, the "pipe" character is usually used to indicate absolute values. The "pipe" is probably a shift-key somewhere north of the "Enter" key on your keyboard. While the "pipe" denoted on the physical keyboard key may look like a "broken" line, the typed character should display on your screen as a solid vertical bar. If you cannot locate a "pipe" character, you can use the "abs()" notation instead, so that "the absolute value of negative 3" would be typed as "abs(–3)".

Here are some more sample simplifications:

Simplify | –8 |.

| –8 | = 8 Copyright © Elizabeth Stapel 2000-2011 All Rights Reserved

Simplify | 0 – 6 |.

| 0 – 6 | = | –6 | = 6

Simplify | 5 – 2 |.

| 5 – 2 | = | 3 | = 3

Simplify | 2 – 5 |.

| 2 – 5 | = | –3 | = 3

Simplify | 0(–4) |.

| 0(–4) | = | 0 | = 0

Why is the absolute value of zero equal to "0"? Ask yourself: How far is zero from 0? Zero units, right? So | 0 | = 0.

Simplify | 2 + 3(–4) |.

| 2 + 3(–4) | = | 2 – 12 | = | –10 | = 10

Simplify –| –4 |.

–| –4| = –(4) = –4

Simplify –| (–2)2 |.

–| (–2)2 | = –| 4 | = –4

Simplify –| –2 |2

–| –2 |2 = –(2)2 = –(4) = –4

Simplify (–| –2 |)2.

(–| –2 |)2 = (–(2))2 = (–2)2 = 4

Sometimes you will be asked to insert an inequality sign between two absolute values, such as:

Insert the correct inequality: | –4 | _____ | –7 |

Whereas –4 > –7 (because it is further to the right on the number line than is –7), I am dealing here with the absolute values. Since:

| –4 | = 4

| –7 | = 7,

...and since 4 < 7, then the solution is:

| –4 | < | –7 |.

When the number inside the absolute value (the "argument" of the absolute value) was positive anyway, we didn't change the sign when we took the absolute value.

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