Current location - Training Enrollment Network - Mathematics courses - There must be two math problems in senior one. Please write down the detailed process of these two questions.
There must be two math problems in senior one. Please write down the detailed process of these two questions.
In the bottom ABCD, EF is perpendicular to OB, plane geometry, self-proof. BB 1 is perpendicular to the bottom ABCD, and EF belongs to the bottom, so BB 1 is perpendicular to EF, and of course EF is also perpendicular to BB 1.

To sum up, EF vertical OB, EF vertical BB 1, OB and BB 1 intersect at b, so we can know EF vertical plane OBB 1.