1. It is known that c is the midpoint of straight line AB, d is the midpoint of AC, and e is the midpoint of BC.

(1) If AB = 18cm, find the length of DE; (2) If ce = 5cm, find the length of DB.

2. It is known that the straight line AB and CD intersect at 0 degrees, the angle COE is a right angle, the angle OF bisection AOE, and the angle COF=34 degrees, and the angle BOD is obtained.

3. The complementary angle of an angle is 20 degrees smaller than 1/3 of its complementary angle. Find this angle.

1 Solution: (1)∵C is the midpoint of straight line AB, D is the midpoint of AC, and E is the midpoint of BC.

∴ac=bc=ab/2,dc=ad=ac/2,ce=eb=cb/2

∴de=dc+ce=ac/2+cb/2=(ac+cb)/2=ab/2

∫AB = 18cm

∴DE= 18/2=9cm

(2)CE = 5cm，CE=CB/2

∴AC=CB=5*2= 10cm

∫DC = AC/2

∴DC= 10/2=5cm

∴db=dc+cb=5+ 10= 15cm

2

Solution: ∫ The straight line AB and CD intersect at 0 point.

∴∠BOD=∠AOC

∠∠COE is a right angle, ∠ COE = 34, ∠ COF+∠ FOE = ∠ COE.

∴∠FOE+34 =90, ∠ Fu =56.

∠AOE∠AOF =∠AOC+∠COF =∠AOC+34。

∴∠AOF=∠FOE=56

∴∠AOC+34 =56

∴∠AOC=∠BOD=22

three

Solution: Let the degree of this angle be x, which is derived from the meaning of the question:

90 x =( 180 x)/3-20

90 x = 60 x/3-20

x-x/3=90 -60 +20

2x/3=50

x=75

A: This angle is 75 degrees.