Question: Puzzling about one operation

I download a maple document from 'Recent Questions',"to find the constants of a equation with data x and y are given", then I open it, and click 'run all' comand in the toolbar. It works very well.

But when I put cursor in one line, and pree 'enter' key, it ruturns a different form of the result, as the picture above shows.

I am very puzzling about this, I'm a beginner in maple, can you give me some explainations?

Thank you very much!

 

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