%circles and ellipses
%circle of radius 1
x=[-1:0.05:1];
y=sqrt(1-x.*x);
y1=-sqrt(1-x.*x);
plot(x,y,'b',x,y1,'b')
hold
clear

%ellipse x^2/36+y^2/16=1
x=[-6:0.1:6];
y1=sqrt(16*(1-x.*x/36));
y2=-sqrt(16*(1-x.*x/36));
plot(x,y1,'r',x,y2,'r')
grid
clear

%ellipse x^2/7^2+y^2/16=1
x=[-7:0.1:7];
y1=sqrt(16*(1-x.*x/7^2));
y2=-sqrt(16*(1-x.*x/7^2));
plot(x,y1,'c',x,y2,'c')
clear

%ellipse x^2/5^2+y^2/16=1
x=[-5:0.1:5];
y1=sqrt(16*(1-x.*x/5^2));
y2=-sqrt(16*(1-x.*x/5^2));
plot(x,y1,'m',x,y2,'m')
clear

%ellipse x^2/4^2+y^2/16=1
x=[-4:0.1:4];
y1=sqrt(16*(1-x.*x/4^2));
y2=-sqrt(16*(1-x.*x/4^2));
plot(x,y1,'y',x,y2,'y')
clear

%ellipse x^2/3^2+y^2/16=1
x=[-3:0.1:3];
y1=sqrt(16*(1-x.*x/3^2));
y2=-sqrt(16*(1-x.*x/3^2));
plot(x,y1,'g',x,y2,'g')
clear

%ellipse x^2/2^2+y^2/16=1
x=[-2:0.1:2];
y1=sqrt(16*(1-x.*x/2^2));
y2=-sqrt(16*(1-x.*x/2^2));
plot(x,y1,'k',x,y2,'k')
clear

%ellipse x^2/1^2+y^2/16=1
x=[-1:0.1:1];
y1=sqrt(16*(1-x.*x/1^2));
y2=-sqrt(16*(1-x.*x/1^2));
plot(x,y1,'--b',x,y2,'--b')
clear

%ellipse x^2/7^2+y^2/1=1
x=[-7:0.1:7];
y1=sqrt(1*(1-x.*x/7^2));
y2=-sqrt(1*(1-x.*x/7^2));
plot(x,y1,'--r',x,y2,'--r')
clear

%ellipse x^2/6^2+y^2/9=1
x=[-6:0.1:6];
y1=sqrt(3^2*(1-x.*x/6^2));
y2=-sqrt(3^2*(1-x.*x/6^2));
plot(x,y1,'--c',x,y2,'--c')