Where the Greek letter phi ( φ {\displaystyle \varphi } or ϕ {\displaystyle \phi } ) denotes the golden ratio.[a] The constant φ {\displaystyle \varphi } satisfies the quadratic equation φ 2 = φ + 1 {\displaystyle \varphi ^{2}=\varphi +1} and is an irrational number with a value of
φ = 1 + 5 2 = {\displaystyle \varphi ={\frac {1+{\sqrt {5}}}{2}}=} 1.618033988749....The golden ratio was called the extreme and mean ratio by Euclid, and the divine proportion by Luca Pacioli, and also goes by several other names.[b]
en
