Triangles: Classification and Elements
Discover the fascinating world of triangles — the simplest and most important polygons in geometry!
1. What is a Triangle?
Definition: A triangle is a polygon with exactly 3 sides, 3 vertices, and 3 angles.
- It is the simplest polygon — you cannot make a polygon with fewer than 3 sides
- Formed by connecting 3 non-collinear points (points not on the same line) with segments
- The word "triangle" comes from Latin: tri (three) + angulus (angle)
Interactive Triangle
Interactive visualization — available in the full lesson
2. Parts of a Triangle
Vertices (Вершины)
The three corner points of the triangle
Labeled with capital letters: A, B, C
Sides (Стороны)
Three segments connecting the vertices
Named: AB, BC, CA (or a, b, c)
Angles (Углы)
Three angles formed at each vertex
Named: ∠A, ∠B, ∠C
Interactive visualization — available in the full lesson