2. If the sum of two angles is 90, then the two angles are complementary.

3. Complementarity and complementarity refer to the relationship between two angles. Two complementary or complementary angles are only related to their sum and have nothing to do with their position.

4. If two sides of one angle are relative extension lines of two sides of another angle, these two angles are called antipodal angles.

5. Two sides of one angle are opposite extension lines of two sides of another angle, which is called antipodal angle. Note: Only when two straight lines intersect can antipodal angles be generated, and antipodal angles appear in pairs.

6. Two straight lines intersect to form four angles with common vertices. If a straight line intersects with two straight lines to get eight angles, which is called "three-line octagon" for short, then the positional relationship of the vertices is congruent angle, inner angle and inner angle of the same side.

7. Both angles are on the same side of two straight lines and on the same side of the third straight line (section line). Such a diagonal is called a juxtaposition angle.

8. Both angles are between two straight lines, on both sides of the third straight line (section line). Such a diagonal is called an interior angle.

9. Both angles are between two straight lines and on the same side of the third straight line (section line). Such a diagonal line is called the inner angle of the same side.