Using the Normal vector to distinguish the front/back of the surface.
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Reflection and Refraction
1. Reflect a ray: [url]http://www.geogebratube.org/material/show/id/111895[/url]
[b]2. →One sided surface[/b]
3. Lamp [url]http://www.geogebratube.org/material/show/id/112549[/url]
4. Refract a ray: [url]http://www.geogebratube.org/material/show/id/112931[/url]
