How Eratosthenes
Calculated the Circumference of the Earth 
While Eratosthenes was not the first to estimate the circumference
of the earth, his was the most accurate of the ancient estimates. Here
is how he did it.

Perpendicular Bisector of a Chord 
A chord is a line segment with end points on a circle. When we
construct a perpendicular bisector of a chord, we create a figure with
interesting properties.

Geometry and Numbers 
In ancient Greece nearly all math had roots in geometry. They even did multiplication
geometrically.

The Kite 
The kite is a figure with many interesting properties. Begin exploring the
kite here.

Properties of Right Triangles Incribed in Circles 
There are several interesting relationships between right triangles and their circumscribing circle.

Drawing an ellipse given two circles with the same center. 
An ellipse can be outlined using two circles with the same center.

Constructing an Ellipse Given a Circle and Inscribed Rectangle. 
An ellipse can be outlined using a circle and a rectangle inscribed in the circle.

Geometric Nets
 A 'net' is a two dimensional (flat) figure that can be folded into a three dimensional geometric
shape. You can use these nets to build your own geometric shapes. For best results, print these on card stock. 