Talk:Absolute value

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If x is a negative number, then | x | = − x. This is incorrect. It should read "If x is a negative number, then | - x | = x."

The latest change is an error. If x is a negative number, then -x is a positive number! It was correct before, the absolute value of x, where x is negative, is -x: If x is negative, | x | = − x

I see what you're saying...I think the working just needs to be changed. |-x| = x but if you declare before hand that x is negative to begin with then |x| is negative, but if you say it equals x, x is still assumed negative. Let's just reword the whole thing, shall we? --David B (talk) 20:48, 14 April 2016 (EDT)
How about simply:

or even show all the signs:

What do you think?--David B (talk) 20:51, 14 April 2016 (EDT)

There should not be any signs inside the absolute value bars. That's where we're going off the rails. You should state the range of x, as in "if x is negative" and then show | x |. I know you want to have | -x | mean something like "the absolute value of a negative number" but that's not what it means. It was correct before: "If x is negative, then | x | = -x." You have to think about what it means for a second, but math is like that. MelH (talk) 22:58, 14 April 2016 (EDT)

I see what you are getting at, but you can have a negative number inside ||, it just translates to positive. You see this in just about ever math textbook. --David B (talk) 00:44, 15 April 2016 (EDT)
Sure. But your confusing two things. What you see is statements like | -3 | = 3. That's different from, "for negative x, | -x | = ..." The first is an example, and it's clear. The second is confused. The "for negative x" part says that x IS a negative number, like -3. "| -x |" then becomes a positive number, like 3. Examples with negative constants are fine. Examples with variables that have been asserted to represent negative numbers, which are then negated, not fine. MelH (talk) 02:01, 15 April 2016 (EDT)
That's why I was thinking we should throw out the "for negative x" part to simplify things. I've never been a genius at math, so I'll just leave this up to you. Do what you think is more precise. --David B (talk) 02:07, 15 April 2016 (EDT)