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Perpendicularity of Straight Lines and Planes. Movie.

The model illustrates the definition of perpendicularity of a straight line and a plane. The motorcycle tracks on the plane of a field (plane α) are lines named a, b and c. The line l holding the lamppost is a perpendicular to the plane α. A base of the lamppost is a cross-point of the line l and the plane α.

Draw lines a', b' and c' in the plane α parallelly to a, b, c through the cross-point. We can draw a plane holding the a' and the l. Since the lamppost is perpendicular to the plane α a` and l are perpendicular to each other. Respectively, the line a is the perpendicular to the line l. In the same manner draw such lines for b and c and for any line in the plane α. That is the line l is perpendicular to the plane α. Similar constructions can be made for b, ñ and any other line held by plane α.

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