kill(all)$

van=facebook.com/LearningCalculus$

f(R,%theta):=2*R*abs(cos(%theta))/(sin(%theta));
f(3,atan(3/2));

g(R,%theta):=(2*abs(sin(%theta)^2*abs(cos(%theta))
             -cos(%theta)^3)*abs(R))/
             (cos(%theta)^2*abs(sin(%theta)));
g(3,atan(3/2));

R=3