Question: pi versus the Pi symbol

I am new to Maple 10. When I enter cos(pi) I get cos(pi symbol) as the output. WHen I enter cos(pi symbol) I get -1 as the output. Why doesn't Maple recognize pi as the pi symbol and get me -1? Also I get error with the following but it works when I use the pi symbol instead of pi: plot([sin(x),cos(x)],x=0..2*pi) Can't Maple tell theat pi is same as the pi symbol.
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