Phi (the golden ratio) is a ratio of simple numbers that is important in proportions in nature. art and architecture.
phi = 1.61803399 (approximately, after rounding)
It is determined on a line with a point dividing the line into 2 segments a and b.
phi = a / b = (a + b) / a
If b = 1, then a is the solution to the equation a^2 - a - 1 = 0
