Question 173
A square of $ABCD$ paper unit is folded so that the vertex $A$ touches an arbitrary point $E$ on the $CD$ side. Thus, three right triangles formed by a single layer of paper are obtained. Determine the length of its sides as a function of $x=DE$ and show that the perimeter of the greater triangle is the sum of the perimeters of the other two, and is half the perimeter of the square. (hace theorem) 