The area of ??a triangle is the base times the height divided by two.
Triangle perimeter formula: The perimeter of a triangle is the sum of its three sides. A closed figure formed by three line segments in the same plane but not in the same straight line connected end to end is called a triangle.
Common triangles are divided into isosceles triangles and unequal triangles according to their sides; they are divided into right-angled triangles, acute-angled triangles, obtuse-angled triangles according to their angles.
Properties of triangle angles:
1. The sum of the interior angles of a triangle on the plane is equal to 180° (sum of interior angles theorem).
2. The sum of the exterior angles of a triangle on the plane is equal to 360° (Sum of Exterior Angle Theorem).
3. The exterior angle of a triangle on the plane is equal to the sum of its two non-adjacent interior angles.
4. There are at least two acute angles among the three interior angles of a triangle.
5. In the triangle, at least one angle is greater than or equal to 60 degrees, and at least one angle is less than or equal to 60 degrees.
6. In a right triangle, if an angle is equal to 30 degrees, then the right-angled side opposite the 30-degree angle is half of the hypotenuse.