# Geometry - Proof, Constructions, Points, Lines, And Planes, Angles, Parallel Lines And Planes

### ideas formal system

Geometry, the study of points, lines, and other figures in space, is a very old branch of mathematics. Its ideas were undoubtedly used, intuitively if not formally, from earliest times. Walking along a straight line toward a particular destination is the shortest way to get there; lining an arrow up with the target is the way to hit it; sitting in a circle around a fire is the most equitable way to share the warmth. Early humans need not have been students of formal geometry to know and to use these ideas.

As early as 2,600 years ago the Greeks had not only discovered a large number of geometric properties, they had begun to see them as abstract ideas to be studied in their own right. By the third century B.C., they had created a formal system of geometry. Their system began with the simplest ideas and, with these ideas as a foundation, went well beyond much of what is taught in schools today.