kill(all)$

van=facebook.com/LearningCalculus$

A(r,θ):=(2*r^2*sin(θ)+r^2*cos(θ)-r^2)/4$

factor(diff(A(r,θ),θ))=0;

solve(%,θ);

%/cos(θ);

tan(θ)=2;

y/x=atan(2)$

float(atan(2)) * radians;
float(180/%pi*atan(2)) * degrees;