> x(1,eta):=
> -(1/16)*(1-eta)*(1-9*eta^2)+(9/16)*(1-eta^2)*(1-3*eta)*cos(Pi/6)+(9/16
> )*(1-eta^2)*(1+3*eta)*cos(Pi/3):
> y(1,eta):=-(1/16)*(1+eta)*(1-9*eta^2)+(9/16)*(1-eta^2)*(1-3*eta)*sin(P
> i/6)+(9/16)*(1-eta^2)*(1+3*eta)*sin(Pi/3):
> plot1:=plot([x(1,eta),y(1,eta),eta=-1..1],colour=black,scaling=constra
> ined,thickness=2):
> plot2:=plot(sqrt(1-x^2),x=0..1,colour=black,scaling=constrained,thickn
> ess=1):
> plots[display]({plot1,plot2}):
> rr:=x(1,eta)^2+y(1,eta)^2:
> rr:=expand(%):
> rr:=factor(%):
> r:=+sqrt(%):
> L_[2]:=evalf(sqrt(int((1-r)^2,eta=-1..1)));

                       L_[2] := 0.002447333606

> plot(1-r,eta=-1..1);

> 
> 
