The first one: to find the normal vectors of two planes by vectors, as long as it is proved that the normal vectors of the two planes are vertical.

Second, it is proved that a straight line in one plane is perpendicular to two intersecting true straight lines in another plane, and similarly, it is proved that a straight line in this plane is perpendicular to two intersecting straight lines in the original plane at the same time.

I suggest the best vector, simple and easy to find!