Idea 24of 24Builds onSame angles can differ in size
Congruent rectangles and parallelograms
When are two rectangles or parallelograms congruent?
Today you'll discover
- why matching sides are not enough
- why matching angles are not enough
- what has to match
Think firstBoth have sides 6, 4, 6 and 4 cm
Both shapes have sides of 6 cm, 4 cm, 6 cm and 4 cm. Are they congruent?
Decide first, then press Next. Check the sides and the angles.
A 6 cm by 4 cm rectangle P and a leaning shape Q with the same side lengths. Their angles are then shown: four 90° angles in P, 60° and 120° in Q. A dashed copy of P laid on Q does not follow its lean. Then a 6 cm by 4 cm rectangle stood on its end is covered exactly by a turned copy. The last step shows a 6 cm by 4 cm rectangle beside a 6 cm by 5 cm one.
See the whole ideathe big idea and the key word, in one place
The big idea
Rectangles and parallelograms are congruent only when their sides and their angles both match.
Compare themSame sides, different angles: a rectangle and a leaning parallelogram, not congruent. Same angles, different sides: two rectangles of different sizes, not congruent.
Construct a copyTo copy a parallelogram, measure two sides and the angle between them, then draw them with a ruler and protractor.
Key word
- parallelogram
- a four-sided shape whose opposite sides are parallel and equal; a rectangle is one with square corners
Ready to use it?
- Decide whether two rectangles or parallelograms are congruent.