It is known that the plane angle of dihedral angle α - ab - β is an acute angle, C is a point in plane α (it is not on edge AB), D is the projection of point C on plane β, and E is the projection of point C on edge ab

It is known that the plane angle of dihedral angle α - ab - β is an acute angle, C is a point in plane α (it is not on edge AB), D is the projection of point C on plane β, and E is the projection of point C on edge ab

Option B
Make a vertical line from D to AB, AB is perpendicular to F, because CD is perpendicular to AB and DF is perpendicular to AB, so AB is perpendicular to plane CDF, so CF is perpendicular to ab
Let's first look at the right triangle CDF, CF is the hypotenuse, DF is the right angle, so CF > DF
It is easy to know tanceb = CF / Fe, tandeb = DF / Fe
According to CF > DF, angle CEB > angle DEB

In the rectangular room of a hotel, in order to make people feel spacious, a plane mirror as big as the wall is installed on one wall. What is the use of this to achieve this goal?

The plane mirror in the mirror reflection of light is used to expand the field of vision
That's what our teacher said

In the dark house, there is a plane mirror on the table. Behind the mirror is a white wall. When you shine a flashlight on the mirror and the wall, the wall is very bright because the wall has a very good effect on the light______ The mirror is dark because it makes the light shine______ ．

Because the mirror is smooth, what happens is specular reflection, and the reflected light is reflected back against the light of the flashlight; while the white wall is diffuse reflection, and the reflected light is reflected in all directions