Idea 22of 24Builds onBuild a triangle from three sides
Congruent means an exact copy
When are two shapes exact copies of each other?
Today you'll discover
- what congruent means
- why turning or flipping does not matter
- how to test with a traced copy
Think firstTriangle P, and triangle Q turned
Q points a different way. Can it still be an exact copy of P?
Decide first, then press Next. Watch whether the dashed copy covers Q exactly.
Triangle P on the left and triangle Q, turned, on the right. Both are measured: sides 4 cm, 3 cm and 5 cm, angles 37°, 90° and 53°. A dashed copy of P slides across and turns until it covers Q exactly, and a box says it fits: congruent. Then a flipped triangle is covered by a copy flipped over. The last step shows two triangles whose bottom sides are 6 cm and 7 cm.
See the whole ideathe big idea and the key word, in one place
The big idea
Congruent shapes are exact copies: every side and every angle matches, even when turned or flipped.
Moves keep shapes congruentSliding, turning and flipping move a shape without changing its sides or angles, so the moved shape is congruent to the first.
Easy to get wrongLooking alike is not enough. Measure: one side a centimetre longer makes the shapes not congruent.
Key word
- congruent
- exactly the same size and shape, so one fits exactly on the other
Ready to use it?
- Decide whether two shapes are congruent.
- Construct a triangle congruent to a given one.