According to Coxeter and Greitzer, one of the solutions to the Butterfly theorem was submitted in 1815 by W. G. Horner of Horner's method fame.
http://www.cut-the-knot.org/pythagoras/Butterfly.shtml
A Mathematical Droodle
http://www.cut-the-knot.org/Curriculum/Geometry/Eyeball.shtml
Proposition I.1 of Euclid's Elements deals with the construction of an equilateral triangle. Propositions I.4, I.8, and I.26 are what we nowadays would call SAS, SSS, ASA theorems, respectively.
http://www.cut-the-knot.org/triangle/index.shtml
Given a vector V and a point P. A vector can be specified by its direction and length.
http://www.cut-the-knot.org/Curriculum/Geometry/Translation.shtml
Word or story problems give us a first glimpse into how mathematics is used in the real word.
http://www.cut-the-knot.org/arithmetic/WProblem.shtml
Discover geometry by creating shapes from loops of paper
http://www.tryscience.org/experiments/experiments_geometry_athome.html
Do you like math puzzles? Well, here's a great one!
http://pbskids.org/zoom/activities/sci/consecutivenumbers.html
A fractal is a rough or fragmented geometric shape that can be subdivided in parts, each of which is (at least approximately) a reduced-size copy of the whole. Fractals are generally self-similar and independent of scale."
http://mathforum.org/alejandre/workshops/fractal/fractal3.html
Working with a partner, study the following array of numbers. What patterns do you see in the arrangement of the numbers? Describe each pattern using words and symbols
http://mathforum.org/workshops/usi/pascal/patterns_pascal.html
The Polyhedra Essay is the final unit assessment. To receive full points on the essay all of the components of the essay must be addressed.
http://mathforum.org/alejandre/workshops/unit14.html