syms a x y b
f=sqrt((x*cos(a)+y*sin(a)+3*cos(a))^2+(-x*sin(a)+y*cos(a)-3*sin(a))^2)-2*exp((atan((-x*sin(a)+y*cos(a)-3*sin(a))/(x*cos(a)+y*sin(a)+3*cos(a)))+2*log(b))/2);
dfx=diff(f,x);
dfy=diff(f,y);
dydx=-dfx/dfy
dydx =
(-1/2/((x*cos(a)+y*sin(a)+3*cos(a))^2+(-x*sin(a)+y*cos(a)-3*sin(a))^2)^(1/2)*(2*(x*cos(a)+y*sin(a)+3*cos(a))*cos(a)-2*(-x*sin(a)+y*cos(a)-3*sin(a))*sin(a))+(-sin(a)/(x*cos(a)+y*sin(a)+3*cos(a))-(-x*sin(a)+y*cos(a)-3*sin(a))/(x*cos(a)+y*sin(a)+3*cos(a))^2*cos(a))/(1+(-x*sin(a)+y*cos(a)-3*sin(a))^2/(x*cos(a)+y*sin(a)+3*cos(a))^2)*exp(1/2*atan((-x*sin(a)+y*cos(a)-3*sin(a))/(x*cos(a)+y*sin(a)+3*cos(a)))+log(b)))/(1/2/((x*cos(a)+y*sin(a)+3*cos(a))^2+(-x*sin(a)+y*cos(a)-3*sin(a))^2)^(1/2)*(2*(x*cos(a)+y*sin(a)+3*cos(a))*sin(a)+2*(-x*sin(a)+y*cos(a)-3*sin(a))*cos(a))-(cos(a)/(x*cos(a)+y*sin(a)+3*cos(a))-(-x*sin(a)+y*cos(a)-3*sin(a))/(x*cos(a)+y*sin(a)+3*cos(a))^2*sin(a))/(1+(-x*sin(a)+y*cos(a)-3*sin(a))^2/(x*cos(a)+y*sin(a)+3*cos(a))^2)*exp(1/2*atan((-x*sin(a)+y*cos(a)-3*sin(a))/(x*cos(a)+y*sin(a)+3*cos(a)))+log(b)))