% PlotCircle_5.m:   Plot two circles (circles 1 and 3 with radii R1, R3) 
%       tangent to each other at the origin with centers on the x axis 
%       and a third circle (circle 2 with radius R2) tangent to and above 
%       circles 1 and 3.
% Input Radii R1, R2, and R3 of three circles

R1 = input('Enter radius of circle 1: ');
R2 = input('Enter radius of circle 2: ');
R3 = input('Enter radius of circle 3: ');
R4 = input('Enter radius of circle 4: ');

clf;
hold on;                          % do not erase drawn circles
angle = linspace(0,2*pi,100);     % vector of angles at which points are drawn

%  Find center of circle 2 (tangent to and above circles 1 and 3)
g2 = ((R2+R3)^2+(R1+R3)^2-(R1+R2)^2)/(2*(R1+R3));   % temporary variable
cx2 = R3-g2;                           % x coordinate of circle 2 center
cy2 = (R2+R3)*sin(acos(g2/(R2+R3)));   % y coordinate of circle 2 center

%  Find center of circle 4 (tangent to and below circles 1 and 3)
g4 = ((R4+R3)^2+(R1+R3)^2-(R1+R4)^2)/(2*(R1+R3));   % temporary variable
cx4 = R3-g4;                           % x coordinate of circle 4 center
cy4 = -(R4+R3)*sin(acos(g4/(R4+R3)));  % y coordinate of circle 4 center

% Set up the circles
x1 = -R1+R1*cos(angle);  y1 = R1*sin(angle);     % Coordinates of circle 1
x2 = cx2+R2*cos(angle);  y2 = cy2+R2*sin(angle); % Coordinates of circle 2 
x3 = R3+R3*cos(angle);   y3 = R3*sin(angle);     % Coordinates of circle 3
x4 = cx4+R4*cos(angle);  y4 = cy4+R4*sin(angle); % Coordinates of circle 4

%Set up the lines
xl = [-R1 cx2 R3 cx4 -R1 R3 cx2 cx4];
yl = [0 cy2 0 cy4 0 0 cy2 cy4];

% Draw circles and lines
plot(x1,y1,'r',x2,y2,'g',x3,y3,'b',x4,y4,'m',xl,yl,'k');

axis equal;
grid on;