In mathematics, two quantities are in the golden ratio if their ratio is the same as the ratio of their sum to the larger of the two quantities. Expressed algebraically, for quantities ⁠⁠ and ⁠⁠ with ⁠⁠, ⁠⁠ is in a golden ratio to ⁠⁠ if where the Greek letter phi denotes the golden ratio. The constant ⁠⁠ satisfies the quadratic equation ⁠⁠ and is an irrational number with a value of 1.618033988749.... The golden ratio was called the extreme and mean ratio by Euclid, and the divine proportion by Luca Pacioli; it also goes by other names.