1. Definition: If the dihedral angle formed by two planes is 90, then the two planes are vertical.

2. Decision theorem: If one plane passes through the vertical line of another plane, then the two planes are perpendicular to each other.

3. If the projection of any point on one plane on another plane is at the intersection of these two planes, then it is vertical.

Extended data 4. If one of the n parallel planes is perpendicular to one plane, the other planes are perpendicular to this plane.

5. Let the equations of two planes be a1x+b1y+c1z+d1= 0, and A2x+B2y+C2z+D2=0, then a1a2+b/.

Make sure that the two planes are parallel.

1. Two intersecting straight lines in a plane are parallel to another plane, so the two planes are parallel.

2. Two planes perpendicular to the same straight line are parallel.

3. Two intersecting straight lines in one plane are parallel to two intersecting straight lines in another plane, so the two planes are parallel.

Distance formula between two planes

The distance between two planes, of course, refers to two parallel planes. Let two planes

ax+by+cz+d=0

ax+by+cz+e=0

The distance is |d-e|/√(a2+b2+c2)