1.  Below is a right triangle.  Dissect it into three pieces so that you have 1 rectangle and 2 triangles.

 

 

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2.  Now dissect this right triangle into three pieces so that you have 1 rectangle and 2 triangles—with one more condition: the three pieces can be reassembled to make a rectangle:

 

 

[[{"fid":"97","view_mode":"default","type":"media","attributes":{"height":237,"width":502,"class":"media-element file-default"}}]]

 

3.  Dissect this square into 4 triangles, which can be reassembled to make a non-square rectangle: