Video narration
How can a shape look slanted and still follow rules as reliably as a rectangle? A parallelogram is a quadrilateral with both pairs of opposite sides parallel. That parallel structure is doing more work than it first appears. It forces each pair of opposite sides to have equal length, even when the shape leans. And it controls the angles: opposite angles are equal, while neighboring angles are supplementary-meaning together, they make 180 degrees. It is not merely a slanted rectangle. Its parallel opposite sides force the rest of its relationships. The lines joining opposite corners are the diagonals, and they bisect each other: each one cuts the other into two equal halves. So, can you trust a slanted parallelogram without measuring everything? Yes: opposite sides match, opposite angles match, neighboring angles total 180 degrees, and the diagonals divide one another evenly.