1. (2021七上·丰台期末) 补全解题过程．

已知：如图，∠AOB＝40°，∠BOC＝70°，OD平分∠AOC．

求∠BOD的度数．

解：∵∠AOB＝40°，∠BOC＝70°，

∴∠AOC＝∠AOB＋∠BOC＝                   ▲                  °．

∵OD平分∠AOC，

∴∠AOD＝∠                  ▲                  （                  ▲                  ）（填写推理依据）．

∴∠AOD＝                  ▲                  °．

∴∠BOD＝∠AOD﹣∠                  ▲                   ．

∴∠BOD＝                  ▲                  °．