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More Transformations on a Pegboard

Stage: 2 Challenge Level: Challenge Level:2 Challenge Level:2

More Transformations on a Pegboard


You might like to try Transformations on a Pegboard before looking at this problem. Here are some ideas to take this activity some stages further.

You may like to use this interactive pegboard to try out your ideas. Read underneath the interactivity for the challenges!

Full Screen Version
This text is usually replaced by the Flash movie.


One of the challenges was, 'By moving just one peg can you make a right-angled triangle?'. Well, I had a go starting the same way:

Billy

Here are two I found moving one peg each time (from the original):

billy 2



billy 3

And so on and so on ...
How many different right-angles triangles can you get if you stick to a grid of $7$ rows of dots and $9$ columns of dots?

The triangle started off having a base of $6$ and was $3$ high.
Look at the other triangles you have found that have this same base and height.
What can you say about the areas of this set of triangles?
(You might like to draw some more triangles with a base of $6$ and a height of $3$ which don't have right angles to test your ideas.)  

Why do this problem?

This activity offers a good chance to develop concepts surrounding triangles, including their areas. It is an engaging activity which allows pupils to work in twos and to have fruitful disussions.

Possible approach

As we all learn in different ways it would be good to allow learners to explore this activity with a number of aids at their disposal, for example:
Spotted paper in squares
- Nail boards with elastic bands
- The on-screen interactive board
- Squared paper

Encourage them to start with the original shape and move one point at a time to see the results. They will need to do this in a systematic way if they are going to find all the possibilities and it is likely that the group will benefit from discussing some strategies for doing this as a whole. This might also require you to model the first few steps in a particular way of being systematic, for example by moving the "top" corner of the triangle one peg up, then two pegs up etc. You can ask the children what to do next at each stage and talk about what might be "sensible" so that you don't miss any out. They may notice a pattern in the way the possible positions for this point lie so that it might not be necessary to actually test every point on the grid. Depending on the class' experience, you could use a number of ways of checking whether an angle is a right-angle, for example by using a protractor or simply a corner of paper.

When it comes to looking at the areas of sets of triangles (i.e. triangles which have the same base and height), the pupils will have different ways of calculating these areas and these should be acknowledged and shared. Many children will be able to make the full generalisation about areas of triangles with identical base and height through this investigation.


Key questions

How are you exploring where the elastic band can go?
How will you make sure you don't miss any triangles out?
How are you finding the areas of the triangles?
What do you notice about the triangles' areas?

Possible extension

In the original Transformations on a Pegboard problem, one of the challenges was about changing a square into a rectangle so that the area doubles by moving two pegs. You could go on to investigate this further with your class, but rather than find a rectangle, look for any shape which can be made by moving two pegs which has double the area of the square. How many ways can they do this? Sometimes when you've exhausted a lot of ideas you have to change the rules again so here's an idea - keep the same starting square but have a larger grid, so it looks like this:
Tanya2
 
Can the group find some new shapes now that by moving two pegs will double the original area? (No matter what the final shape is!) What would happen if you could only move one peg to double the area?

Possible support

Using nail/peg boards or the interactivity on screen will help all children access this problem, but those with poorly developed motor skills may need help from an adult or fellow pupil.