Triangle is a closed figure composed of three line segments on the same plane but not on the same straight line, which has applications in mathematics and architecture. Acute triangle: all three internal angles of the triangle are less than 90 degrees. Right triangle: One of the three internal angles of a triangle is equal to 90 degrees, which can be recorded as Rt△. Obtuse triangle: One of the three internal angles of a triangle is greater than 90 degrees.
Ordinary triangles are divided into ordinary triangles (three sides are unequal) and isosceles triangles (isosceles triangles with unequal waist and bottom and isosceles triangles with equal waist and bottom, that is, equilateral triangles); According to the angle, there are right triangle, acute triangle and obtuse triangle, among which acute triangle and obtuse triangle are collectively called oblique triangle.
Divide by edge
1, equilateral triangle; An equilateral triangle is mathematically defined as a triangle with three unequal sides.
2, isosceles triangle; An isosceles triangle refers to a triangle with two equal sides, which are called the waist of the triangle. In an isosceles triangle, two equal sides are called waist and the other side is called bottom. The angle between the two waists is called the top angle, and the angle between the waist and the bottom edge is called the bottom angle.
The two base angles of an isosceles triangle are equal (abbreviated as "equilateral angles"). The bisector of the vertex, the midline of the bottom and the height of the bottom of an isosceles triangle coincide (referred to as "the three-line unity property of an isosceles triangle"). The bisectors of the two base angles of an isosceles triangle are equal (the median lines of the two waists are equal and the heights of the two waists are equal).