syms k
t = 0:0.1:2*pi;


r = 2;
res = [];
xpos = [];
rd = 6:1:20;
x = r*cos(t);
y = r*sin(t);
amx = [];
ag = [];
% x采样点
sx = xc+r;
for xc = rd
    x1 = r*cos(t)+xc;
    y2 = r*sin(t)+yc;
    xpos = [];
    res = [];
    for j = t
        xi = r*cos(j);
        yi = r*sin(j);
        result = solve(abs(k*xc-yc-k*xi+yi)/sqrt(k^2+1)==2);
        tmp = real(result);
        g = double(tmp(tmp~=0));
        grad1 = g(1);
        grad2 = g(2);
        if abs(grad1) < grad2
            g1 = -grad2;
            g2 = grad2;
        else 
            g1 = grad1;
            g2 = abs(grad1);
        end
        xpos = [xpos xi];
        res = [res abs(atand(g1) - atand(g2))];
    end
    [~,idx] = max(res);
    mx = xpos(idx);
    qx = r*2*r/xc;
    ag = [ag qx];
    amx = [ amx mx];
end

figure()
plot(amx,'or')
hold on
plot(ag)