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## 'Gnomon Dimensions' printed from http://nrich.maths.org/

You may wish to try the related problem

Building Gnomons
first.

A Gnomon is a rectangle with another rectangle cut out of one corner. The area of each Gnomon is a Fibonacci
number. (The Fibonacci numbers are $1, 1, 2, 3, 5, 8$ and so on, with each new term being the sum of the
previous two terms.)

$G_1$ has area $3$, $G_2$ has area $5$, $G_3$ has area $8$ and so on.

Draw the next three gnomons in the sequence.

Look at the length and width of the large rectangle from which each gnomon is made.

Is there a pattern to the lengths and widths?

Can you generalise?

Now look at the length and width of the rectangle cut out of each gnomon. Can you see any patterns
here? Can you generalise and justify what you see?

I want to group the gnomons with area 3, 8 and 21 together, and the gnomons with area 5, 13 and 34
together. Can you explain why I want to divide these into two separate groups?

Can you give a convincing argument why all the gnomons fit into one of these two groups?

The interactivity below may help you to think about this problem.

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What other interesting patterns and relationships can you find? Send us your ideas and justifications.