Prove that the straight line is perpendicular to the plane. As long as two groups of straight lines are perpendicular to the plane, 1 is often used to prove the property theorem of straight line perpendicular to the plane. 2. See an isosceles or equilateral triangle, find its midpoint, and make the three lines vertical; 3. See the Pythagorean inverse theorem commonly used in the data to calculate the angle =90 degrees, that is, vertical. Standardizing writing steps with decision theorem. After learning the space vector, we can prove verticality by dot product =0. 5 Some people use plane geometry to calculate the angle =90 degrees. It is rarely seen in other college entrance examinations and simulations.