Comparing Quantities | Class 7 Mathematics Notes

Introduction to Triangles

A triangle is the most basic closed geometric shape, formed by three line segments joining three points called vertices. Each pair of vertices is connected by a side, resulting in three sides and three vertices. The three sides meeting at the vertices create three angles inside the triangle, known as the angles of the triangle. Triangles come in various shapes and sizes, such as equilateral, isosceles, scalene, right-angled, acute-angled, and obtuse-angled triangles. The notation for a triangle is typically Δ followed by the vertices, for example, ΔABC. The angles at the vertices are denoted as ∠A, ∠B, and ∠C, corresponding to vertices A, B, and C respectively. The naming order of vertices can vary without changing the triangle's identity. Understanding triangles is fundamental in geometry, as they form the basis of many geometric principles and constructions.

📊 Diagram: Figures showing various types of triangles and the notation of vertices and angles; See figure_1, figure_2, figure_3, figure_4.

🧪 Activity: Observe different triangles and practice naming them by their vertices in various orders.

🔗 Connection: This section introduces the basic properties of triangles, leading to the next section on constructing equilateral triangles using geometric tools.