function plotictan
hold on; 
grid on; 
axis([-10,10,-10,10]);
[x0,y0] = ginput(1);
plot(x0,y0,'z')
c=atan(y0)-x0;
s=-pi/2-c:pi/100:pi/2-c;
f=dsolve('Dy=1+y^2', 'y(a)=b', 'x');
h=subs(f, {'a','b','x'}, {x0,y0,s});

end

