Video narration
If you turn a square paper cut-out, is it still a square? A square, a rectangle, and tilted versions of both are straight-sided figures. On a rectangle, each edge is a side; opposite sides face each other. The corners are vertices, and the openings at the corners are angles. Check the labels: AB equals CD, and AD equals BC. Each pair is equal, and all four angles are 90 degrees. For a square, AB, BC, CD, and DA are all equal, and all four angles are 90 degrees. So, a rectangle has equal opposite sides; a square has four equal sides. Both have four 90-degree angles. Pause and classify: (a) all sides equal, all angles 90 degrees; (b) opposite sides equal, all angles 90 degrees; (c) a figure that fails the required properties. Think now. [Thinking pause.] Answers: (a) square; (b) rectangle- a square also meets those properties; (c) neither. Turn the paper square, then the rectangle. Their position changes, not their side lengths or angles. To name square PQRS, follow its edge: PQRS, QRSP, RSPQ, SPQR. PQSR jumps out of order, so it is not a boundary name. Memory card: square, all sides equal and all angles 90 degrees; rectangle, opposite sides equal and all angles 90 degrees; naming follows the boundary; rotation changes position, not properties. Last question: four right angles, but unequal opposite sides-is that a rectangle? Pause. [Thinking pause.] Yes, your turned paper square is still a square. Four right angles alone aren't enough: a rectangle also needs equal opposite sides.