When you have an element making a circular motion (let's take perfect circle right now), when you look at its motion from the side you will see that element moving from center position up, staying there, and then going down again through center point and under it, then again staying there and going higher.
Does that sound familiar? It should.
It's sinusoidal motion in function of time.
When you will have ((sin(t*x))*y), where t is time, then whatever you put into x will stretch sinusoid graph horizontally (will make it hit tops and bottoms less/more frequently) and y will make those tops and bottoms either more, or less extended from point 0,0 (where rotation have its center).
And here we have that +160 at the beginning: using sin(), or cos() will give us back location of rotation's center in x=0 and y=0 so we need to add something to compensate for it (eg.: when we want to have the center in the middle of a 320x320 screen we add 160).