Chris Impens defines the number [math]\varphi[/math](phi) as the positve number to which the condition applies: [math]\frac{1}{\varphi}=1+\varphi[/math].[br]He adds that it's not necessary to define [math]\varphi[/math] as a ratio of sides or parts of a segment.[br]In Pythagorean time geometry and algebra weren't distinct disciplines. Numbers too were depicted graphically.[br]While learning about fractions we also work with parts of chocolate or pizza's, but don't always continue illustrating [math]\frac{1}{2}[/math] starting from the construction of the perpendicular bisector of a segment.

The reverse of [math]\varphi[/math] is represented with the symbol [math]\Phi[/math] (= capital letter Phi).[br]As a value you find [math]\Phi=\frac{1}{\varphi}=\frac{1+\varphi}{2}=1.618...[/math]