1, and the sum of the interior angles of the triangle is equal to 180 degrees.

2. The sum of any two sides of a triangle must be greater than the third side, which also proves that the difference between any two sides of a triangle must be less than the third side.

3. The sum of squares of two right angles of a right triangle is equal to the square of the hypotenuse, which is the Pythagorean theorem.

The bisector of any angle in a triangle divides this angle into two equal small angles.

5. The sum of the distances from a point outside the triangle to the three vertices is equal to the sum of the distance from the point to the midpoint of the opposite side and the distance from the point to the vertical foot.

6. The sum of the distances from one point in a triangle to the two endpoints of the opposite side is equal to the difference between the distance from this point to the midpoint of the opposite side and the distance from this point to the vertical foot.

7. The difference between the distances from a point to three vertices in a triangle is equal to the difference between the distance from the point to the midpoint of the opposite side and the distance from the point to the vertical foot.

8. Draw an arc with any point as the center and any length as the radius. The obtained bad arc intersects with two straight lines parallel to the bottom, and the distance from the intersection point to the center is equal to the chord length of the arc.

The knowledge about triangles is as follows:

1, a triangle, is a basic figure in mathematics, which consists of three line segments that are not on the same straight line, end to end. According to the length or angle of sides, triangles can be divided into ordinary triangles, isosceles triangles, right triangles, acute triangles and obtuse triangles. In an isosceles triangle, if an angle equals 60 degrees.

Then this triangle is an equilateral triangle. For a right-angled triangle, if an acute angle is equal to 30 degrees, the right-angled side it faces is equal to half of the hypotenuse. In addition, there is an important theorem: the line segment between two points is the shortest, that is, the sum of any two sides of a triangle is greater than the third side. In a triangle, the line segment connecting the vertex and the midpoint of the opposite side is called the midline.

3. In addition, the sum of the internal angles of the triangle is 180 degrees, and each angle corresponds to two sides, which is called the opposite side of the angle. There are many knowledge points related to triangles, such as congruent triangles, bisector of triangle angle, perpendicular bisector, isosceles triangle and equilateral triangle, right triangle, Pythagorean theorem and so on.