[Test.4] A point is said to divide a line segment in extreme and mean ratio, of in golden section, when the longer of the two segments formed is the mean proportional between the shorter segment and the whole line. The ratio of the shorter segment to the longer segment is called the golden ratio.

The Pythagoreans showed consederable inferest in the golden section and the golden ratio.
The wymbol of the Pythagorean brotherhood was the pentagram, of 5_pointed_star, formed by the 5 diagonals of a regular pentagon.
Show that the golden ratio is (¡î5-1)/2.