X=85:-1:50;
    Y=5:1:40;
    Xr=X*pi/180;
    Yr=Y*pi/180;
    N=(Xr.*cosd(Y))-(Yr.*cosd(X)); 
    D=(cosd(Y)-cosd(X));            
    C=N./D;
    
    for j= length(C);
    y= @(F) (F*pi/180)+cotd(F)-C(j);
    end
 
    FL=30;
    FR=70;
    
        for i= 1:1000
          FM=(FL+FR)/2;
            if y(FL)*y(FM) < 0
              FR=FM;
            else
              FL=FM;
            end
          if abs (y(FL)) < 1.0E-10;        
          break
          end
        end
    
    
  fprintf('Number of iterations: %d\n', i);
  fprintf('phi_note: %f\n', FL);