**Plane geometry**is geometry in the two-dimensional Euclidean space

**R**

^{2}, also called the 'geometrical plane'.

For all practical purposes one may imagine an infinitely big piece of flat paper.

Despite being so familiar to most of us, much is still to be discovered in this area, and new mathematical results are still found all the time in plane geometry.

Topics:

- trigonometry
- polygons
- tilings