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A Greek letter commonly used to represent functions, angles, or scalar fields in mathematics and physics.

\varphi image

Examples

Angle in geometry or trigonometry

\sin(\varphi) = \frac{\text{opposite}}{\text{hypotenuse}}

Golden ratio definition

\varphi = \frac{1 + \sqrt{5}}{2} \approx 1.618034

Euler's totient function

\varphi(n) = \#\{k \in \mathbb{N} : 1 \leq k \leq n, \gcd(k,n) = 1\}