If M is the midpoint of AC, n is the midpoint of BC, and ab = 10cm, the length of Mn is obtained

If M is the midpoint of AC, n is the midpoint of BC, and ab = 10cm, the length of Mn is obtained

AB = 10cm, so BC = 2Ab = 20cm
So AC = AB + BC = 30cm
M is the midpoint of AC, so cm = AC / 2 = 15cm
N is the midpoint of BC, so CN = BC / 2 = 10cm
So Mn = cm-cn = 5cm