Cut three points a, B and C on the line a in order, so that ab = 8cm and BC = 5cm. If O is the midpoint of the line AC, find the length of the line ob

Cut three points a, B and C on the line a in order, so that ab = 8cm and BC = 5cm. If O is the midpoint of the line AC, find the length of the line ob

AC = AB + BC = 13, O is the midpoint of line AC, so Ao = 6.5
OB=AB-AO=8-6.5=1.5

Given the line AB = 5cm, cut BC = 2cm on the line AB, and D is the midpoint of AC, then the length of line BD is________
Line AB is divided into three parts: 2:3:4. The distance between the middle points of the first part and the third part is 4.2cm, and the longest part is 4.2cm_____ cm.

>Given the line AB = 5cm, cut BC = 2cm on the line AB, and D is the midpoint of AC, then the length of line BD is________
Because it's on line AB, there are two positions of C
When C is in the middle of AB (arranged in ACB, the figure is abbreviated), AC = 5-2 = 3, and D is the midpoint of AC, then DC = 3 / 2 = 1.5, so BD = DC + CB = 1.5 + 2 = 3.5
When C is outside AB (arranged by ABC, the figure is abbreviated), AC = 5 + 2 = 7, and D is the midpoint of AC, then DC = 7 / 2 = 3.5, so BD = dc-cb = 3.5-2 = 1.5
>Segment AB is divided into three parts: 2:3:4. The distance between the middle points of the first part and the third part is 4.2cm, and the longest part is 2.5cm_____ cm.
The distance between the midpoint of the first part and the third part = half of the length of the first part + half of the length of the second part + half of the length of the third part
According to the known conditions, half of the length of the first part + half of the length of the third part = the length of the second part
So the length of the second part is 4.2cm/2 = 2.1cm
The length of the longest part is 2.1cm/3 * 4 = 0.7cm * 4 = 2.8cm

Take three points a, B and C successively on a straight line, ab = 5cm, O is the midpoint of line AC, and ob = 1.5cm, then the length of BC is () cm
A. 6B. 8C. 2 or 6D. 2 or 8

According to the meaning of the title, as shown in the figure, ∵ AB = 5cm, OB = 1.5cm, ∵ OA = AB + ob = 6.5cm. ∵ o is the midpoint of AC, ∵ OC = OA = 6.5cm, ∵ BC = ob + OC = 8cm; as shown in the figure,