1, angle method. Make a right triangle composed of oblique line, vertical line and projection of oblique line on the plane, and find the angle formed by oblique line and projection according to the conditions.

2, three cosine relation method. Find or draw a special straight line with oblique feet on the plane, try to find the angle between this straight line and projection and its angle with diagonal "or other chords", and use the three cosine relation to find the cosine value of the line-plane angle, so as to get the required value.

3. Projection method. When the length of a line segment and its projection on the plane are known, the cosine value of the angle can be directly obtained by using its length ratio.

4. Dialectical methods. It is proved that the straight line is perpendicular to the plane, and the included angle between the straight line and the plane is 90.

Solution of surface angle (dihedral angle);

1, definition method (dihedral angle definition)

2. Three perpendicular lines method

3. Projection area method

Pay attention to the line-plane angle conversion and confirm each other.