Mike, in your book you wrote |a| = -a ? I thought the absolute value could only be a positive number.

I think you’re referring to this table:

All I’m really trying to do there is remind you that when a number is less than zero, taking its absolute value means changing its sign. For example, say the *a* in the number line above is –5. Obviously you know that |–5| = 5, but that also means that if *a* = –5, then |*a*| = –*a*, because –*a* = –(–5) = 5.

Does that help?