How to find a point where line touches circle

Hi, In below mentioned code, How to find a point if line touches circle where it touches, if not how find it.Please help me in finding. x1=5; y1=5; r = 10; t = 0 : .1 : 2*pi; x = r * cos(t) + x1; y = r * sin(t) + y1; hold on; plot(x, y); x2=10; y2=10; %line x3=20; y3=20; line([x2,x3],[y2,y3]) hold off

Thanks, Sita