sinus/cosinus shoot

Hi !

How to do this ? When the player shoot, the bullet follow this kind of path. i'm searching a formulae to do this ! Thanks for your help !

Graphics 640,480
y=480
initialx=320
xw#=4
While y>0
	y:-1
	a:+4
	xw#:+0.25
	x=initialx+Sin(a)*xw
	Plot x,y
Wend
Flip
WaitKey

Thanks Chris !