Typo in Real Analysis Study Page: Absolute Value of x for x<0?

[starkind]

I found a study page which lists the absolute value of x for x<0 as -x. I think this has to be a typo. The study area is real analysis. Does anyone have better information? Maybe it is some special notation?

 

[quasar987]

I'm pretty sure this is the standard definition.

|x| = x if x>=0 and -x if x<0

 

[starkind]

Ouch. I thought absolute value was a difference expressed as a positive number.

I see in wikipedia that an absolute value is always positive. But the notation seems to indicate otherwise. What gives?

arghh. I see it now. The notation is saying to reverse the sign of a negative number. Thanks

 

[Diffy]

Ouch. I thought absolute value was a difference expressed as a positive number.

I see in wikipedia that an absolute value is always positive. But the notation seems to indicate otherwise. What gives?

arghh. I see it now. The notation is saying to reverse the sign of a negative number. Thanks

It is. If x < 0 say x = -5 then you would want the |x| = 5 which is -x.