One: Triangle
1, triangle: A figure composed of three line segments that are not on the same line end to end is called a triangle.
2. Trilateral relationship: the sum of any two sides of a triangle is greater than the third side, and the difference between any two sides is less than the third side.
3. Height: Draw a vertical line from the vertex of the triangle to the line where the opposite side is located, and the line segment between the vertex and the vertical foot is called the height of the triangle.
4. midline: in a triangle, the line segment connecting the vertex and its relative midpoint is called the midline of the triangle.
5. Angular bisector: The bisector of the inner angle of a triangle intersects the opposite side of this angle, and the line segment between the vertex and the intersection of this angle is called the angular bisector of the triangle.
Two: congruent triangles
Basic definition:
1, conformity: Two graphs that can completely overlap are called conformity.
Congruent triangles: Two triangles that can completely coincide are called congruent triangles.
3. Corresponding vertices: The mutually coincident vertices in congruent triangles are called corresponding vertices.
4. Corresponding edges: The overlapping edges in congruent triangles are called corresponding edges.
5. Correspondence angle: The mutually coincident angles in congruent triangles are called correspondence angles.
Three: Axisymmetric
Basic concepts:
1. Axisymmetric graph: If a graph is folded along a straight line, the parts on both sides of the straight line can overlap each other, and this graph is called an axisymmetric graph.
2. Two figures form an axis symmetry: fold one figure along a straight line if it can match the other.
If two figures overlap, then they are said to be symmetrical about this line.
3. The midline of a line segment: the line passing through the midpoint of the line segment and perpendicular to the line segment is called the midline of the line segment.
4. isosceles triangle: A triangle with two equal sides is called an isosceles triangle. Two equal sides are called waist, the other side is called bottom, the included angle between the two sides is called top angle, and the included angle between bottom and waist is called bottom angle.
5. equilateral triangle: A triangle with three equilateral sides is called an equilateral triangle.