3. The main part of the triangle
Discussion: ① Define the intersection of ②×× lines-the property of the× center of triangle.
① High line ② Middle line ③ Angle bisector ④ Middle vertical line ⑤ Middle line.
⑵ General triangle ⑵ Special triangle: right triangle, isosceles triangle and equilateral triangle.
4. Determination and properties of special triangles (right triangle, isosceles triangle, equilateral triangle and isosceles right triangle)
5. congruent triangles
(1) Determine the consistency of general triangles (SAS, ASA, AAS, SSS).
⑵ Determination of congruence of special triangle: ① General method ② Special method.
6. Area of triangle
⑴ General calculation formula ⑴ Properties: The areas of triangles with equal bases and equal heights are equal.
7. Important auxiliary lines
(1) The midpoint and the midpoint form the midline; (2) Double the center line; (3) Add auxiliary parallel lines
8. Proof method
(1) direct proof method: synthesis method and analysis method.
(2) Indirect proof-reduction to absurdity: ① Counterhypothesis ② Reduction to absurdity ③ Conclusion.
(3) Prove that line segments are equal and angles are equal, often by proving triangle congruence.
(4) Prove the folding relationship of line segments: folding method and folding method.
5. Prove the sum-difference relationship of line segments: continuation method and truncation method.
[6] Prove the area relationship: indicate the area.
Third, quadrilateral.
1. General Properties (Angle)
⑴ Sum of internal angles: 360.
(2) Parallelogram connecting the midpoint of each side in turn.
Inference 1: Connect the midpoints of the sides of the quadrilateral in turn with equal diagonal lines to get a diamond.
Inference 2: Connect the midpoints of the sides of the quadrilateral in turn with diagonal lines perpendicular to each other to get a rectangle.
⑶ Sum of external angles: 360.
2. Special quadrilateral