sin(10x) + cos(9x). Or better yet, we could animate
sin(10x+t) + cos(9x+t) as t varies. Here
is the result:
The images above were generated with the following Mathematica code:
Table[Plot[Sin[10x+t] + Cos[9x+t], {x,-2Pi,2Pi},
Axes->None, AspectRatio -> Automatic, PlotPoints -> 300],
{t,0,2Pi-Pi/6,Pi/6}]
The images were then assembled into an animated gif using
GifBuilder.