#### Topic: how do i use pi?

I´m having trouble with using pi.

I want to plot a function as follows:

f(x) = (pi((2*pi-x)^2/(4*pi^2))(sqrt(1-((2*pi-x)^2)/(4*pi^2)))/3)

...but i only get error message.

When I write:

f(x) = (3.14((2*3.14-x)^2/(4*3.14^2))(sqrt(1-((2*3.14-x)^2)/(4*3.14^2)))/3)

...it works fine.

What could be the problem?

thanks in advance!