2. Multiply one factor by several and divide another factor by several, and the product remains unchanged.

3. At least four small squares can form a big square.

4. At least 8 small cubes can be used to make a big cube.

5. The sum of consecutive odd numbers starting from 1 is a square number.

6, the characteristics of square and rectangle:

* * * Similarity: Both a square and a rectangle have four sides, four right angles, and the opposite sides are equal.

Difference: The four sides of a square are equal, that is, the adjacent sides are equal.

Relationship: Square is a special rectangle.