How do i invert math.sin to be spiky instead of a circle?

I'm trying to make a missile trajectory but it just make triangle because they use the same math.sin

Missile: Image

The white line are the intended trajectory The red line are the trajectory that the missile took.

So my question is... how do i do to turn this circle Image to this Image

The normal circle is math.sin

How do you turn the circle to be like the second image?