It is known that M is a fixed point on the fixed length line segment AB, and C and D are two

Solution: 1) Set the exercise time t

md=mb-3t，ac=am-t

md=3ac

mb-3t=3am-3t

mb=3am，am=1/4ab

an=am+mn，bn=bm-mn

an-bn=am-bm+2mn=mn

am-bm=-mn

am=1/2mn

mn=1/2ab

mn/ab=1/2

an=ab+bn

an-bn=mn

ab=mnmn/ab=1

mn/ab=1/2

I wish you progress in your studies!! Hope!

It's so hard, it looks awesome.

Because ab=12cm, m is the midpoint of the front good belt ab, so Huilu searches am=mb=6cm with socks, and because c is on mb and mc:cb=1:2, so mc=2cm, cb=4cm, ac=am+mc=6+2=8cm

The line section is 10 units long, and there are 4 single positions from M to point A.

C to point A 5 units.

The hail of the feast is mc = one unit.

So one unit = 2cm

10 units = 20cm

So AB is 20 cm long.

By the way, for the landlord, cm is centimeter.

Do it with a compass ruler.

Known line segment ab c

Lengthen A, measure the line segment B with a compass, take the right end of the A line segment as the starting point, and cut off the length of B on the right side of the ray ruler A and punctuate it with a pen.

Measure the length of the line segment C with a compass, take the right end of the line segment B as the starting point, cut the length of C on the right side of the ray, and punctuate it with a pen.

Line segment m is done.

Solution: 1) Set the exercise time t

md=mb-3t，ac=am-t

md=3ac

mb-3t=3am-3t

mb=3am，am=1/4ab

an=am mn，bn=bm-mn

an-bn=am-bm 2mn=mn

am-bm=-mn

am=1/2mn

mn=1/2ab

mn/ab=1/2

an=ab bn

an-bn=mn

ab=mnmn/ab=1

mn/ab=1/2

I wish you progress in your studies!! Hope!

There are two cases:

1) m is in the middle of cd, so, cd = 1 2ab = 5

2) m is outside cd, so, cd = 1 2 (am bm) = 5