Light reflects off a curved surface by forming [color=#a61c00][i]equal angles[/i][/color] ([color=#85200c][i]incidence [/i][/color]and [i][color=#85200c]reflection[/color][/i]) [color=#85200c][i]with the tangent[/i][/color] at the point it falls on the surface.[br][br]If we consider the ellipse as a reflecting surface, when a [color=#1155cc][i]ray of light emitted from one of the foci[/i][/color] meets a [color=#1155cc][i]point on the ellipse[/i][/color], it will [color=#1155cc][i]reflect[/i] [/color]off the ellipse and [color=#1155cc][i]pass through the other focus[/i][/color].[br][br][br]Start the animation in the applet below to view this optical property of the ellipse. [br]If you [b]Show details[/b], you will see the geometry behind this property: move the point of incidence [math]P[/math] to verify that the property holds for all points of incidence on the ellipse.