Math՚s: Lines and Angles: Triangle: Meaning, Types and Properties (For CBSE, ICSE, IAS, NET, NRA 2022)

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Triangle- Meaning

A triangle is a closed figure formed on a plane by joining three collinear points by three-line segments. It has six elements-

  • Three angles formed on the three points. ∠ A, ∠ B and ∠ C in the given figure.
  • Three sides that consist of the three-line segments. AB, BC and AC in the given figure.
Triangle Meaning

Types of Triangles

Triangles can be classified into different types on two bases-

On the Basis of Sides

  • Equilateral triangle: A triangle in which all the three sides are equal is called an equilateral triangle.
  • Isosceles triangle: A triangle in which two sides are equal is called an isosceles triangle.
  • Scalene triangle: A triangle in which all sides are of different lengths, is called a scalene triangle
Types of Triangles

On the Basis of Angles

  • Obtuse angled triangle: A triangle in which one of the angles is an obtuse angle is called an obtuse angled triangle or simply obtuse triangle.
  • Right angled triangle: A triangle in which one of the angles is a right angle is called a right-angled triangle or right triangle.
  • Acute angled triangle: A triangle in which all the three angles are acute is called an acute angled triangle or acute triangle.
Types of Triangles

Properties of Triangles

Angle Sum Property of a Triangle- The sum of all the three angles of a triangle is . Thus, in ,

Properties of Triangles
  • The angle formed by a side of the triangle produced and another side of the triangle is called an exterior angle of the triangle. Corresponding to an exterior angle of a triangle, there are two interior opposite angles. Interior opposite angles are the angles of the triangle not forming a linear pair with the given exterior angle.
  • An exterior angle of a triangle is equal to the sum of the two interior opposite angles. In
Properties of Triangles

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