(1) direct method: find a straight line perpendicular to the plane and find the direction vector of the straight line.

(2) The undetermined coefficient method: establish a spatial rectangular coordinate system.

Normal vector is a concept of spatial analytic geometry. The vector represented by a straight line perpendicular to a plane is the normal vector of the plane. Normal vector is suitable for analytic geometry. Because there are countless straight lines perpendicular to the known plane in space, each plane has countless normal vectors (including two unit normal vectors).

The main applications of normal vectors are as follows:

1. Find the angle formed by the oblique line and the plane (generally only sine value can be found): Find the normal vector of the plane and one side of the oblique line, and then simultaneous equations can be used to get the cosine value of the angle. According to the formula Sinα=|Cosα|. This principle can also be used to prove that straight lines and planes are parallel.

2. Find the dihedral angle: find the angle formed by the normal vectors of two planes, which is equal to or complementary to the dihedral angle.

3. Distance from point to surface.