Divide a paper into equal parts
A piece of paper can easily be divided into equal parts. As for 2, 4, or 8 parts, this is very straightforward. But you can also divide a paper into 3, 5, 6, or 7 parts without using a ruler. It is also quite simple to prove the correctness of the resulting partition:
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The intersection of f and g can be calculated by solving the equation f(x) = g(x) ⟷ 2x = -x + ½ ⟷ x = ⅙
Folding instructions
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Divide a paper into fifths and sevenths
To divide a paper into seven rectangles of equal size, the paper is divided into thirds first.