The origin of the Greek letter **φ** (phi) is unclear but it could have been derived from the ancient Phoenician letter
𐤒 (qōp).

In mathematics, 𝜑 is a symbol for the golden ratio, an irrational number with approximate value of 1.61803. The symbol was proposed by Mark Barr after the Greek sculptor Phidias (Φειδίας) who is said to have employed it in his creations. 𝜑 is a solution of the polynomial equation *x*^{2} − *x* − 1 = 0.

The regular pentagram includes five acute and five obtuse isosceles triangles. In all of them, the ratio of the longer side to the shorter side is 𝜑.

More photos of letters, numbers and sea glass @ Shutterstock.

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