Mathematics surely starts with counting and basic arithmetic; perhaps some understanding of repetition and regular intervals comes next, but geometry was surely not far behind. It was surely where mathematics first got axiomatised, at least; and several ancient civilisations recognised the significance of some of its consequences. In this part of my web-site, I explore some of the basic results of classical geometry, particularly those involving pictorial proofs (presented using SVG images, for the most part). More algrebraic treatments of geometry remain elsewhere.

- Conventional markings and simple results
- Isosceles triangles (with two edges of equal length) and some properties of circles
- The three centres of a triangle
- Pythagoras's theorem and its diverse proofs
- Basic trigonometry, angles and their units
- Rectangles whose diagonals trisect corners
- How to construct a regular pentagon

I'm a bit haphazard about adding to and maintaining this area.

Things I should illustrate and/or prove:

- Apollonius's theorem: (x+y)**2 + (x−y)**2 = 2.(x**2 + y**2)
- Draw a line from a point on a circle to meet a diameter at right angles; the length of this line is the geometric mean of the two parts into which it cuts the diameter.