Video narration
On your paper rectangle, will PR and QS match in length-and do their corner cuts always match? Join opposite corners: the diagonals. Predict, then measure with a ruler: PR = QS. Use a protractor at P, R, Q, and S; compare the labeled angle pairs. Repeat on wide, tall, and almost-square rectangles. Lengths match; angle splits vary. A square is special. Remember: join, measure, compare. A right angle can split into 60° and 30°: 60° + 30° = 90°. Can you construct that on your paper?