Intersection line: When two lines intersect, they form an angle. The degree of this angle can be measured with a protractor. The included angle between two intersecting lines is usually called "intersection angle".

Parallel lines: When two lines are parallel, they will intersect at infinity, thus forming a right angle (180 degrees). The included angle of parallel lines is called "parallel angle".

Slope: Slope can be used to describe the angle of a straight line relative to the X axis. The greater the slope, the greater the angle between the straight line and the X axis.

Perpendicular: When two lines are perpendicular, they form a right angle (90 degrees). The included angle between vertical lines is usually called "vertical angle".

Parallelogram: A parallelogram is a quadrilateral composed of two groups of parallel lines. Diagonal angles of parallelogram are equal and adjacent angles are complementary.

Trapezoid: Trapezoid is a geometric figure with four sides, two of which are parallel and the other two are not parallel. Diagonal complementation of trapezoid.

Knowledge expansion:

Angle is a basic concept in mathematics and geometry, which represents the included angle between two rays in a geometric figure. The size of an angle can be expressed in degrees or radians.

In plane geometry, an angle usually consists of two rays or line segments. The common endpoint of these two rays is called the vertex of the angle, and these two rays are called the edge of the angle. According to the definition, an angle can be regarded as a plane part between two rays drawn from a point.

The size of an angle can be expressed in degrees or radians. A complete circle is 360 degrees in degrees, so the right angle is 90 degrees. In radians, a complete circle is 2π radians, so a right angle is π/2 radians.

Angle is a very important concept in trigonometric function. Trigonometric functions such as sine, cosine and tangent are all related to angle. For example, sine function sin(x) represents the sine value of angle x, cosine function cos(x) represents the cosine value of angle x, and tangent function tan(x) represents the tangent value of angle X.

In addition to the common angle system, there is also a system called radian, which represents the angle with the radius of the circle as the benchmark length unit. One radian equals an angle of 57.3, so a complete circle is 2π radians. In the polar coordinate system, the position of a point can be determined by distance and angle, where the angle is expressed in radians.

In practical application, the concept of angle is widely used in various fields, including engineering, machinery, physics, astronomy, geography and so on. For example, in mechanical manufacturing, the precision control of angle is very important; In physics, concepts such as angular velocity and angular momentum all involve angle; In astronomy, the concept of angle is often used in the position and movement of stars.

In a word, angle is a basic concept in mathematics and geometry, which represents the included angle between two rays in a geometric figure. The angle can be expressed in degrees or radians, which is widely used in various fields.