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.