Point A is outside the plane VBC, and it is known that AV is perpendicular to VB and AV is perpendicular to VC.
Therefore, AV is perpendicular to the plane VBC (a straight line is perpendicular to two intersecting straight lines in a plane, so this straight line is perpendicular to the plane where the two intersecting straight lines are located-the judgment theorem that straight lines are perpendicular to the plane).
It is also known that BC is a straight line in the plane VBC;
So AV is perpendicular to BC (if a straight line is perpendicular to a plane, it is perpendicular to any straight line in the plane-the property theorem that a straight line is perpendicular to a plane).