Triangle ABC is a right angled triangle with the hypotenuse AB = 17 and the leg BC = 8. Hence, its other leg AC is= = = 15 units long. The segment MN is the midline in this triangle, parallel to the leg AC. Hence, the length of the segment MN is half the leng of the leg AC, i.e. 15/2 = 7.5 units. ANSWER