Simon has just discovered **copycats**. A square is a copycat because you can put four of them together to make another square.

Simon wonders if triangles and circles are copycats. What do you think?

This problem explores tessellation: covering a plane surface by the repeated use of a single shape, without gaps or overlapping. Students are challenged in the first instance to identify shapes that tessellate (squares and triangles) and those that do not (circles).

The 'copycat' idea in this problem involves students in using tessellating squares to make a larger square, which is a 'copycat' shape of the smaller square(s), and tessellating triangles to make a larger triangle that is the same shape. This prompts the investigation of square numbers, 1, 4, 9, 16, 25 and so on.

The extension challenges students to find other shapes that tessellate to form a larger 'copycat' shape.

### Problem

Simon has just discovered **copycats**. A square is a copycat because you can put four of them together to make another square.

Simon wonders if triangles and circles are copycats. What do you think?

### Teaching sequence

- Ask:
*What is a copycat?* - Discuss the definition of copycat as it applies to this problem.
- Give the students (in pairs) an equilateral triangle and ask them to find out whether it is a copycat. Discuss the properties of an equilateral triangle (3 equal sides, 3 equal angles )
*How do you know that they are equal?*(fold and check*)* - Share findings.
- Pose the problem: Are all triangles copycats?

The students need to make their own triangle and see if it is a copycat. As they work ask:*What type of triangle are you using?*(right triangle, scalene, isoceles, equilateral)*Describe the triangle that you are using?*

Are circles copycats? Why do you think that? - Share findings.

#### Extension to the problem

- Simon talks to Ben about his copycats. Ben notices that you need four squares to make a bigger square and four triangles to make a bigger triangle. Can you make a square with any other number of squares? How many squares can you put together to make a square? Is there a pattern here?
- What other shapes are copycats?

#### Solution

All triangles are copycats. This can be shown using four triangles as in the picture.

On the other hand, circles aren’t copycats. Clearly two or more circles don’t tessellate to make a circle becasue there are always gaps.

#### Extension 1:

Any square number of squares 4, 9, 16, 25 can be used. Why can’t a non-square number be used? Is this the same for triangles too or do you have to use triangle numbers there?

#### Extension 2:

The L-shape in the drawing below is a copycat. To check this out, put one L-shape around each of the top-left, bottom-left and bottom-right corners.