Why modulus sign omitted?

[yellup]

I can't understand why the modulus sign is omitted (line 11-12 from top, the picture attached) anyone can explain?
Besides im new to this forum so if i had broken some rules pls bear with me. Any help is appreciated :grin:

 

[yellup]

Finally I understand, apparently the publishers have skipped some steps, thx for taking time viewing my nonsense post.

 

[stapel]

When would \(\displaystyle e^{x^2+c}\) ever be negative? So why would the absolute-value bars be necessary?

 

[yellup]

Actually I see it this way..

Hi stapel, (Dunno how to greet forgive me if i greet inappropriately),
Actually I see it this way (in the attachment), because at line 20, they got A=-1 as the answer (after the substitution), but at line 14, they take A=e^c which means that A will never smaller than zero.
Besides if the modulus is removed without any additional explanation, it is like saying there's no solution if (y-3)/(x+2) is smaller than zero while in reality there is. Correct me if im wrong.

 

[stapel]

...at line 20, they got A=-1 as the answer....

I hadn't read the first scan all the way to the end. I hadn't noticed that they'd arrived at a negative value for \(\displaystyle e^c\). As such, yeah, I think they erred in not either retaining the absolute-value bars or else using a "plus-minus" sign (as you did) to allow for the negative value of \(\displaystyle A\).

Sloppy and lazy work on their part. Sharp work on your part!