@acer It's the first time that I know such a difference. Thanks for your help.

@tomleslie  Thanks for you explaination

@Ramakrishnan  Dear, I　haven't been online for a few days. Thanks for your help. it's really nice of you all.

@acer  I really need to learn more about "assuming". Thanks for your comment.

@acer  Thanks for your  kind reminding. (1/2) is not the same with 0.5. I got this point.

My original problem is like this.  I will upload one picture and a file to explain more conveniently.

1. why is the expression (6)  not the same with the sum of expressions (4) and (5)
2. in expression (5), How to make "4ln(e)-1=3". simplify doesn't work
   

ask.mw

@gkokovidis 

are you still online?  I wanna describe my question further.  Here is the capture of screen and my file named "ask".

Why the equation (6) is not the same with the sum of equation (4) and (5). Thanks

ask.mw

@gkokovidis you really do me a big favor.  I never know  "assuming" . So far, I'm not sure whether it can completely solve my problem. But it really gives me the right direction. Thanks

@acer  Sorry for confusing you.  Let me explain again.

it's obviously ( x^2)^0.5=x.

However, when I do it  in Maple. It is like this. The result is not x. That's my question. Is it clear?