# Absolute values

Can someone give me a n00b lesson in absolute values, i though i remembered, but i don't.

I got stuck on a

$$-|-8|$$ Related Introductory Physics Homework Help News on Phys.org
Chi Meson
Homework Helper
Read this as "negative one times the absolute value of negative eight."

zat help?

HallsofIvy
Homework Helper
What is |-8|?

What is the negative of that?

Chi Meson said:
Read this as "negative one times the absolute value of negative eight."

zat help?
this is integers right?

so uhm..
$$-1|-8| = 7$$ ?

TD
Homework Helper
No, the absolute value means that you "make the number positive", if it's negative.

It can be defined by saying:
|x| = x if x ≥ 0
|x| = -x if x < 0

Which is just a more mathematical way of saying that positives stay positive and negatives become positives.

A few examples may help:
|2| = 2
|-3| = 3
|0| = 0
|-5/3| = 5/3

Now, you can solve yours?

-|-8|= 8

right?

TD
Homework Helper
What is |-8| ? And then again a -, since it say - (|-8|)

TD said:
What is |-8| ? And then again a -, since it say - (|-8|)

Chi Meson
Homework Helper
that's right.

Thank you ^.^ so can i get a laymens explanation(if that is possible) on how this answer is achieved?

Last edited:
EnumaElish
Homework Helper
-(|-8|) is two functions nested: g(f(-8)) where f(x) = |x| and g(y) = -y. With nested functions you begin to peel the onion from the inside, as it were. So you first figure f(-8) is |-8| which is 8 (why?). Then you substitute this answer for y = f(x), inside g and now you have g(8) = -8. Make sense?

HallsofIvy
Homework Helper
Do you see where you went wrong with the first one?
$$-1|-8| = 7$$

I think you recognized that |-8|= 8 but then you subtracted 1

-|-8| or -1|-8| does not mean subtract the two numbers- it means multiply!

HallsofIvy said:
Do you see where you went wrong with the first one?
$$-1|-8| = 7$$

I think you recognized that |-8|= 8 but then you subtracted 1

-|-8| or -1|-8| does not mean subtract the two numbers- it means multiply!
thank you.