I'm Brazilian teacher and I have just entered this forum. My English is very poor, but I'll try to explain my doubt.
I study hyperbolic geometry and I have the book "Introduction to Non-Euclidean Geometry", by Harold E. Wolfe. I love this book, but some exercises are making me crazy. In the chapter about Saccheri Quadrilateral, there is a exercise that says:
Prove that, if perpendiculars are drawn from the extremities of one side of a triangule to the line passing through the midpoints of the other two sides, a Saccheri Quadrilateral is formed. (page 81)
How can I prove that? In the NonEuclid software is easy to see this, but prove is hard.