Ellipse by Paper Folding
Ellipse by Paper Folding
Let be the center of a circle with radius and let be a point inside the circle. Choose a point on the circumference. Let be the intersection of the perpendicular bisector of and line . Then . So the point is on the ellipse with foci and and the sum of the distances from to the foci is .
G
r
A
B
C
AB
GB
AC+CG=BG=r
C
A
G
C
r
To construct a tangent on the ellipse, fold the circle so that the circumference touches the point .
A