Cutting it Out

I cut this square into two different shapes. What can you say about the relationship between them?
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Problem



So, I started with a $10$ by $10$ green square,
I marked the half-way point along the top edge,
I then drew a line from that point to a corner at the base.
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Cutting it Out
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Cutting it Out
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Cutting it Out
Then I cut the corner piece out along that line and made a change of colour, so I ended up with these two shapes:


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Cutting it Out
What can you say about these two shapes?
Can you say something about the relationship between them?
Do you have any other ideas about these two shapes?


What about starting with a rectangle like this ...

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Cutting it Out


Then you could mark it at half-way or elsewhere ...

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Cutting it Out
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Cutting it Out
What can you say now?