Question

如图,已知∠BOC=2AOB,OD平分∠AOC,若∠BOD=20°,求∠AOB的度数.

Answer 1

因为,

∠BOD = ∠AOD - ∠AOB

= (1/2)∠AOC - ∠AOB

= (1/2)(∠AOB + ∠BOC) - ∠AOB

= (1/2)(∠AOB + 2∠AOB) - ∠AOB

= (1/2)∠AOB,

所以,

∠AOB = 2∠BOD = 40°