∠∠COB =∠AOB-∠AOC
∠∠AOB = 180,∠ AOC = 40。
∴∠COB= 180 -40 = 140
Oe division ∠BOC
∴∠COE= 1/2∠BOC=70
∠∠DOE =∠DOC-∠COE
∠∠Doc = 90,∠ COE = 70。
∴∠DOE=20
(2) Write the answer directly: 1/2α (that is, α, not A)
(3)① Conclusion: 2∠DOE=∠AOC
∠∠COB =∠AOB-∠AOC
Once again ∵OE division ∠COB
∴∠EOC= 1/2∠COB
= 1/2(∠AOB-∠AOC)
∵? ∠DOE=∠COD-∠EOC
=90 - 1/2∠COB
= 90- 1/2∠AOB+ 1/2∠AOC
= 90- 1/2 * 180+ 1/2∠AOC
∴2∠DOE=∠AOC
②2∠AOF+∠BOE = 1/2(∠AOC-∠AOF)
4∠AOF+2∠BOE=∠AOC-∠AOF
5∠AOF+2∠BOE = 2∠ doe
5∠AOF+∠COB=2∠DOE
5∠AOF+∠AOB-∠AOC=2∠DOE
5∠AOF+∠AOB=2∠DOE+∠AOC
5∠AOF+∠AOB=4∠DOE
∴5∠AOF+ 180 =4∠DOE
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