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Khan Academy
Khan Academy: Quadrilateral Overview
This video tutorial [8:24] defines what a quadrilateral is and identifies and defines concave quadrilaterals, convex quadrilaterals, trapezoids, parallelgrams, rectangles, rhombi, and squares.
Khan Academy
Khan Academy: Quadrilaterals: Quadrilateral Overview
This video identifies and defines concave quadrilaterals, convex quadrilaterals, trapezoids, parallelgrams, rectangles, rhombi, and squares.