Gaokao 高考 ＝ Baccalaureate = Cambridge GCE A-Level
Hint:
f(x+1) = 2f(x)
tells the height = f(x) double when x moves to x +1
=> periodicity is 1
Like Sine or Cosine curves have periodicity of 2π.
sin (2π + A) = sin (A)
Ref: More complicated curve drawing by French Method.
Mathtuition88 