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I. Distance and Angle; Triangles and Quadrilaterals. Distance between points and angle between lines. The triangle. Principle of duality; coparallelograms and cotrapezoids. Proof s of the principle of duality.
When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.