파일:Pentagon.svg

${\displaystyle (l-x):x=x:l}$

if

${\displaystyle l='1}$

then

${\displaystyle x^{2}+x-1=0}$

${\displaystyle x={\frac {{\sqrt {5}}-1}{2}}}$

or

${\displaystyle 1-x={\frac {3-{\sqrt {5}}}{2}}}$

${\displaystyle x:1-x\approx 0.618:0.382\approx 8:5}$

or

${\displaystyle 1:x=1:{\frac {1+{\sqrt {5}}}{2}}}$

${\displaystyle {\frac {1+{\sqrt {5}}}{2}}\approx 1.618}$