Several ways of defining the Golden Ratio allow either, or both. One convention is that upper-case Phi or Φ is 1.618[...], while lower-case phi or φ is 0.618[...].

The values are related by φ = 1/Φ, as well as Φ = φ + 1. Both of these relations can be derived from the fact that they are the ratios of a Golden Rectangle--if a square has length one, then adding a rectangle with height φ to the side will give a rectangle of length Φ, and the rectangles are Similar.

It's its brothe (more accurately its inverse), usually written Phi with a bar on top. They both respect the golden ratio.

He probably confused it with 1/phi and didn’t check his equation.

TIL 1/phi=phi-1

That's essentially the definition. φ is the solution to

    φ^2 - φ - 1 = 0

Which can be re-arranged, by dividing by φ to,

    φ - 1 - 1/φ = 0

or:

    1/φ = φ - 1

Or

φ^-1=φ-1

Yes, φ^-1 is another way to write 1/φ.

Yeah but the 【 ａｅｓｔｈｅｔｉｃｓ】

Happy phi day ^_^