The usual formulation for x and y being in golden proportion is

; the right-hand side clearly is greater than 1. Taking y = 1 gives

An illustration is given by the 72-72-36 degree isosceles triangle. The bisector of one of the 72-degree angles divides the opposite side in golden ratio; calling x the length of the base and y the length of the smaller segment of the side opposite the angle bisector, gives the above proportion.