1. Line-plane verticality: If a straight line is perpendicular to any straight line in the plane, it is said to be perpendicular to the plane.

2. General formula: let tan(a/2)=t, Sina = 2t/( 1+t 2), COSA = (1-t2)/(1+t2), Tana = 2t/(65438+). Product sum and difference: sina * cosb = [sin (a+b)+sin (a-b)]/2, cos a * sinb = [sin (a+b)-sin (a-b)]/2, cos a * cosb = [cos (a+b)+cos.

3. If two non-coincident planes have a common point, then they have one and only one common straight line passing through the point.

4. Monotonicity, parity and periodicity of the function. For example, monotonicity definition: note that the definition is relative to a specific interval. There are defined methods (difference comparison and quotient comparison). Derivative method (for polynomial function).

If two planes are perpendicular to each other, the straight line perpendicular to their intersection on one plane is perpendicular to the other plane.