From the top B of the trapezoid ABCD, lower the height BH.
Since the trapezoid is rectangular, and BH is the height, then the quadrangle BCDH is a rectangle, then BH = CD = 3 s, BC = DH.
In a right-angled triangle ABH, we determine the length of the leg AH.
AH ^ 2 = AB ^ 2 – BH ^ 2 = 25 – 9 = 16.
AH = 4 cm.
Then AD = AH + DH = 4 + 5 = 9 cm.
Let’s define the middle line of the trapezoid.
KM = (BC + AD) / 2 = (5 + 9) / 2 = 14/2 = 7 cm.
Answer: The middle line of the trapezoid is 7cm.
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