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Khan Academy
Khan Academy: Properties of Shapes
Identify and compare shapes based on their attributes. Shapes include triangle types, quadrilateral types, pentagons, and hexagons. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video...
National Council of Teachers of Mathematics
Nctm: Illuminations: Angle Sums
Students may use this computer applet to explore angle sums of triangle, quadrilaterals, pentagons and hexagons.