Given that the line segment AB = 10cm, there is a point C on the line AB, and BC = 2cm, M is the midpoint of the line segment AC, then am=______ ．

Given that the line segment AB = 10cm, there is a point C on the line AB, and BC = 2cm, M is the midpoint of the line segment AC, then am=______ ．

① When point C is on the extension line of segment AB, AC = AB + BC = 12 and∵ m is the midpoint of segment AC, then am = 12ac = 6; ② when point C is on segment AB, AC = ab-bc = 8 and∵ m is the midpoint of segment AC, then am = 12ac = 4

There are three points a, B and C on the straight line, ab = 10cm, BC = 40cm, M is the midpoint of AC, then am = () cm

Sub situation
① 25cm (a --- B --- m --- C) as shown in the figure, M is the midpoint of AC, am = 25
② 15cm (b --- a --- m --- C) as shown in the figure, ab = 10, BM = 25, am = 15