1. When two straight lines intersect, there is only one common vertex, and both sides of two angles are opposite extension lines. Such two angles are called vertex angles which are diagonal to each other. Two straight lines intersect to form two pairs of vertex angles. The two opposite angles are equal.

2. Angles can be divided into acute angle, right angle, obtuse angle, right angle, rounded corner, negative angle, positive angle, upper angle, lower angle and zero angle.

3. In geometry, an angle is a geometric object composed of two rays with a common endpoint. These two rays are called the edges of an angle, and their common endpoint is called the vertex of the angle.

The two corners have a common edge, and their other side is an extension line with opposite directions. The two angles with this relationship complement each other.

5. The two corners are on the same side of the cut line and the same side of the two cut straight lines. Diagonal lines with this positional relationship are called juxtaposition angles.