𠃋BEF=70𠃋B=70 𠃋DCE=140且CD//AB求𠃋CEF=
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![𠃋BEF=70𠃋B=70 𠃋DCE=140且CD//AB求𠃋CEF=](/uploads/image/z/6946513-25-3.jpg?t=%26%23131275%3BBEF%3D70%26%23131275%3BB%3D70+%26%23131275%3BDCE%3D140%E4%B8%94CD%2F%2FAB%E6%B1%82%26%23131275%3BCEF%3D)
𠃋BEF=70𠃋B=70 𠃋DCE=140且CD//AB求𠃋CEF=
𠃋BEF=70𠃋B=70 𠃋DCE=140且CD//AB求𠃋CEF=
𠃋BEF=70𠃋B=70 𠃋DCE=140且CD//AB求𠃋CEF=
40°
因为 ∠BEF=70°,∠B=70°,所以AB∥EF
故 CD∥EF
将cd延长s,因为,∠DCE=140°所以 ∠SCE=40°
又因 CD∥EF
所以 ∠CEF=40°