Math's: Lines and Angles: Triangle: Meaning, Types and Properties

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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

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

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

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

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

Properties of Triangles

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