Here we present some notes on elementary geometry, basically the geometry of Euclid, except we avail ourselves of the use of algebra. Here is some foundational material.
The complex plane and the Euclidean plane
The construction of the regular dodecahedron, and the associated icosahedron, is one of the high points in Euclid’s Elements. See these notes for a Cartesian take on how this is done.
The pentagon, the dodecahedron, and the icosahedron
Click here for figures for these notes.
Next we have a proof of Heron’s formula for the area of a triangle.