[quote author=Fu-Kwun Hwang link=topic=46.msg5225#msg5225 date=1262238350]
Refraction obey Snell's Law n_1\sin\theta_1=n_2\sin\theta_2
[/quote]

what i mean is the equation "x^2/n+y^2/n=1"

i dun see the snell's law in it?