Never.
No. The planes must either coincide (they are the same, and intersect everywhere), be parallel (never intersect), or intersect in exactly one line.
A dihedral angle is the angle between two intersecting planes.
no
Two planes do not intersect at all if the planes are parallel in three-dimensional space.
Never.
A line, or intersecting planes.
Intersecting planes!
yes
No, two planes do not intersect in exactly one plane unless the planes are exactly overlapping, making one plane. In Euclidean Geometry two planes intersect in exactly one line.
Two distinct planes will intersect in one straight line.
No, 2 planes may only intersect at a line, a plane, or not at all. THREE planes may intersect at a point though...
No. The planes must either coincide (they are the same, and intersect everywhere), be parallel (never intersect), or intersect in exactly one line.
No. Either they do not intersect at all, or they intersect in a straight line or are the same.
A dihedral angle is the angle between two intersecting planes.
Some planes are parallel and don't intersect at all. Those that do intersect (and that are not coincident, i.e. the same plane) intersect in a line.
no