How does delphi PI get it?

How does delphi PI get it? Delphi/Windows SDK/API
Http://www.delphi2007.net/DelphiBase/html/delphi_20061205223540274.html
I want to use PI computing in Delphi. Can I directly call a function?
Do I have to write a constant Pi = 3.141592653?

I don't know if there is a constant definition in math. Pas? I am not eager to install Delphi here...

With this constant
Pi
System Unit

How to call it? Specific points

Oh, in that unit,

You just need to reference that unit in uses.

How can I add System in uses?
'Redeclared: 'system' Error

Well, it indicates that uses is already in use.

Directly use the PI constant to check if it is available

Showmessage (floattostr (PI ));

No, the return value is 0.
What is going on?

I just installed DELPHI6 and tried it. It's all right ..
If you have not solved the problem, pasteCode

Pi is about 3.14159265358979323846264338327950288
Oh... I used to recite this.

OK