Folded paper showing dimensions for solution The fold is made along BE. A folds onto A`.

A`B = AB = Ö2 Þ A`C = 1 (by Pythagoras)

DA`BC is therefore a right-angled isosceles triangle.

Þ ÐBA`C = 45° Þ ÐEA`D = 45°

Þ ED = A`D = Ö2 - 1