Problem deal with Saccheri quadrilaterals. You may use results about triangle congruence,...

Problem deal with Saccheri quadrilaterals. You may use results about triangle congruence, but you may not use Euclid’s Parallel Postulate or any of its equivalents.

A Lambert quadrilateral is one that has three right angles. It can be shown that the fourth angle is not obtuse. In the Lambert quadrilateral ABCD shown, prove that CD ≤ AB. (hint: Suppose that AB < CD. Let E be a point on , consider ∠BED, and observe that ABED is a Saccheri quadrilateral.)