In fact, the line connecting the midpoints of two opposite sides of the isosceles trapezoid is the height of the isosceles trapezoid, which is the be in the figure; The line connecting the midpoint of the two waists is half of the sum of the upper and lower bottoms of the isosceles trapezoid, that is, 1/2(AB+CD). Turn △BCE to △DAF,

In this way,1/2 (ab+CD) =1/2 (FB+de) = de, and the sum of squares of two groups of relative midpoint lines of an isosceles trapezoid is 8, which can be expressed as de 2+be 2 = 8, while in a right triangle BDE, de 2+be 2 =