Classifying Shapes: From Circles to Quadrilaterals

Khan Academy

This educational video provides a clear, step-by-step guide to identifying and classifying common two-dimensional geometric shapes. Starting with basic curves like circles and ovals, the narrator progresses to polygons, specifically triangles and the diverse family of quadrilaterals. The video uses hand-drawn visuals to demonstrate the specific attributes—such as side length, corner angles, and parallel lines—that define each shape. A significant portion of the video is dedicated to the hierarchy and classification of quadrilaterals. It explains complex relationships between shapes, such as why a square qualifies as both a rectangle and a rhombus, and distinguishes between general quadrilaterals, rectangles, rhombuses, and trapezoids. The narrator uses visual proofs, like drawing square corners to test for right angles and extending lines to test for parallel sides, to make abstract definitions concrete. This resource is highly valuable for elementary mathematics classrooms introducing geometry concepts. It moves beyond simple shape recognition to deep conceptual understanding of geometric attributes. Teachers can use this video to introduce vocabulary like "parallel," "right angle," and "quadrilateral," or to clarify common misconceptions about shape classification, such as the idea that a square is a distinct category separate from rectangles.