ABSTRACT
This chapter suggests a consistent usage of 'side', 'edge', 'face', 'corner' and 'vertex'. There is nothing absolute about the suggestion, and it is not enshrined in 'official' mathematics. Thus triangles have three sides, rectangles four sides, and so forth. Polygons are closed shapes with three or more straight sides. 'Polygon' is one of the most general terms for shapes that primary pupils learn. However, it does not cover all the 2-D shapes they encounter. Children well draw polygons with 90 or even 360 sides to simulate circles. A shape has 'line symmetry' if the shape on one side of the line 'mirrors' the shape on the other. A paper shape could be folded along a line of symmetry, and the edges would match precisely. Alternatively, a mirror could be placed along the line, and the part visible, plus its reflection in the mirror, would look just the same as the original shape.
