The first volume of grade seven, the first volume of grade seven, the first volume of grade seven, chapter four, chapter four, review, review, necessary knowledge, 1. Related concepts and properties of lines, rays and line segments. (1) Line segment: Of all the straight lines between two points, the line segment is the shortest. (2) Ray: The line segment extends infinitely in one direction to become a ray, and the ray has an endpoint. (3) Straight line: A straight line is formed by a line segment extending infinitely in two directions. A straight line has no end points, only one straight line passes through two points. 2. Midpoint of a line segment: The point that divides a line segment into two lines with equal dirt is called the midpoint of the line segment. 3. Distance between two points: The length of the line segment between two points is called the distance between these two points. 4. Definition of angle, measurement of angle and comparison of classification angle. The bisector of an angle is a graph composed of two rays with a common endpoint. A graphic measurement method formed by a ray rotating from one position to another around its endpoint: superposition method: first, the vertices of two angles coincide, one side coincides with the other side, and then the positions of the other two sides are compared to determine the size of these two angles. This is to compare the size from the aspect of "shape". Fillet: 1 fillet =3600=2 flat angle =4 flat angle: 1 flat angle = 1800=2 Cartesian right angle: 1 right angle =900 acute angle: obtuse angle less than right angle: angle greater than right angle but less than right angle, a ray. (1) Parallel lines: Two lines that do not intersect in the same plane are called parallel lines. (2) After passing a point outside the straight line, there is one and only one straight line parallel to this straight line. (3) If two straight lines are parallel to the third straight line, the two straight lines are also parallel to each other. 6. The concept of verticality and its related properties. (1) verticality: when one of the four angles formed by the intersection of two straight lines is a right angle, two straight lines are said to be perpendicular to each other, and one straight line is called the perpendicular of the other straight line, and its intersection point is called the vertical foot. The perpendicularity of a straight line is a special case where two straight lines intersect. (2) The nature of the vertical line: ○ 1 passes a little and only one straight line is perpendicular to the known straight line. ○2 Of all the line segments connecting a point outside the straight line with each point on the straight line, the vertical line segment is the shortest. 7. The length from a point outside a straight line to the vertical section of the straight line is called the distance from the point to the straight line.