Missing square and how I have been tricked!
This morning, my deskmate brought a triangle wooden board to school, which consisted of 4 different pieces. He took all of the pieces and rearranged 4 of them in a different order. The interesting thing is that it missed one square, although the big triangle was still the same size
He did not give me the answer, and I still could not figure that out myself (That was totally insane but now I will share with you that "paradox"):
At first, this seems like a paradox, but the thing that is inaccurate here is the assumption that this figure is a triangle while it is a quadrilateral.
These above three points are not linear as these two triangles are not similar: 5/2 is different from 8/3. The tangents of those two small angles were approximately the same, making it looks like those three dots are linear.