Folding a rectangular sheet of paper into thirds using the crossed ladders problem The optic equation of the crossed ladders problem can be applied to folding rectangular paper into three equal parts . & One side ( the left one illustrated here ) is partially folded in half and pinched to leave a mark. The intersection of a line from this mark to an opposite corner  with a diagonal  is exactly one third from the bottom edge. The top edge can then be folded down to meet the URL
Folding a rectangular sheet of paper into thirds using the crossed ladders problem The optic equation of the crossed ladders problem can be applied to folding rectangular paper into three equal parts : + = therefore; 2 + 1 =&therefore; h = = One side ( left in the illustration ) is partially folded in half and pinched to leave a mark. The intersection of a line from this mark to an opposite corner (red) with a diagonal (blue) is exactly one third from the bottom edge. The top edge can then be folded down to meet the URL
R
.
: + =
A
therefore; 2 + 1 =
A
therefore; h = =
R
the left one illustrated here
left in the illustration
A
(red)
A
(blue)