A technician often has to sketch or design ductwork and the other parts of an HVAC system. Sometimes you have to sketch the room or building you are working with. This means working with lines, angles ...

Polygons are multi-sided shapes with different properties. Shapes have symmetrical properties and some can tessellate. Loci and constructions - AQA Loci are a set of points with the same property.

IN modern treatises on crystallography, the crystal is imagined projected radially on the surface of a sphere, and the spherical triangles so obtained are dealt with by spherical trigonometry.