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### Number phi (*φ*)

The golden ratio is an irrational number with the value *φ* = 1,61803398874989…

##### Explanation

You can calculate the golden ratio as

With the quadratic formula you get

with as positive solution

and as negative solution

As the numbers *a* and *b* are both positive, the negative solution is not valid.

##### Additional information

The letter *φ* (phi) is from the old Greek sculpter Phidias, who wrote a book about the golden ratio.