clear all

t = 0:0.01:2;

L0 = 0.5;
x1 = 0.5*ones(1,length(t));
x2 = 0.5 + 0.25*cos(2*pi*t);

for i=1:length(x1),

a = acos( (L0^2 + x1(i)^2 - x2(i)^2)/(2*L0*x1(i)) );

Xp(i) = x1(i)*cos(a);
Yp(i) = x1(i)*sin(a);

plot([0 Xp(i)],[0 Yp(i)],'b-','linewidth',4)
hold on
plot([L0 Xp(i)],[0 Yp(i)],'r-','linewidth',4)
plot(Xp,Yp,'k.')
plot(0,-0.02,'k^','markersize',10,'markerfacecolor','k')
plot(L0,-0.02,'k^','markersize',10,'markerfacecolor','k')
plot(0,0,'ko','markersize',10,'markerfacecolor','w')
plot(L0,0,'ko','markersize',10,'markerfacecolor','w')
plot(Xp(i),Yp(i),'ko','markersize',10,'markerfacecolor','w')
hold off
text(0.02,0,'A','fontsize',12)
text(L0+0.02,0,'B','fontsize',12)
text(Xp(i)+0.02,Yp(i),'P','fontsize',12)
axis([-0.1 0.6 -0.1 0.6])
axis square
grid on
pause(0.01)

end