If M and N are the midpoints of the non-parallel sides of a trapezoid, it makes sense to call the segment MN the midline of the trapezoid. Why? (It actually should be called the midsegment, of course. Strange to say, some textbooks call it the median). Suppose that the parallel sides of a trapezoid have lengths 7 and 15. What is the length of the midline of the trapezoid? What are the lengths of the three pieces into which the midline is divided by the points where it intersects the diagonals of the trapezoid?