Puzzle on the triangle.

In triangle top four figures that have to be repositioned to form the "triangle" without a unit square.

How to explain this?

Thank's.

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Note: in the top "triangle" the three points are $(0,0),(8,3),(13,5)$, so that IF they were on a line the slopes 5/13 and 3/8 would have to match. But they don't.