High school math. If the face is vertical, can I push the line directly?
It can be inferred that the two planes are perpendicular, so a straight line perpendicular to the intersection of the two planes in one plane is perpendicular to the other plane. And "if two planes are perpendicular, then the straight line in one plane that is not perpendicular to the intersection of the two planes (this condition is very important) must not be perpendicular to the other plane."