Congruent shapes have exactly the same shape and size, so all corresponding side lengths and angle measures match, even when one shape is moved, turned, or flipped and appears in a different position or orientation. The understanding distinguishes congruence from sharing only a color, number of sides, or general appearance and applies to familiar two-dimensional shapes, supporting later work with geometric properties and measurement.
Two shapes are congruent if they have exactly the same shape and size. One shape may be moved, turned, or flipped, but its measurements must still match the other shape.
Example:
Shape A is a rectangle with side lengths units and units. Shape B is also a rectangle, but it has been turned. Its side lengths are units and units.
To decide whether they are congruent:
Compare the side lengths.
Shape A has sides measuring and units.
Shape B has sides measuring and units.
The lengths match when Shape B is turned to line up with Shape A.
Compare the angles.
Both rectangles have four right angles.
Ignore the position.
Shape B looks different only because it has been turned. Turning a shape does not change its shape or size.
Therefore, the two rectangles are congruent. They have matching side lengths and matching angles.
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