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2.3 Types of triangles

Triangles are classified into various types, using two different parameters - the lengths of their sides and the measure of their angles.

Length of the Side

Based on the lengths of their sides, triangles are classified into three categories.

  1. Equilateral triangle : If the lengths of all three sides of the triangle are equal, then it is called an equilateral triangle. Figure 2.3 shows an equilateral triangle.

    Figure 2.3

  2. Isosceles triangle : If only two sides of a triangle are equal in length, it is called as an isosceles triangle. Figure 2.4 shows an isosceles triangle.

    Figure 2.4

  3. Scalene triangle : If all the sides of a triangle have different lengths it is called a scalene triangle. Figure 2.5 shows a scalene triangle.

    Figure 2.5

Angles

  1. Acute triangle : A triangle in which all the angles are acute, ( i.e. < 900 ) is called as an acute triangle. Figure 2.6 shows an acute triangle.

    Figure 2.6

    A special case of an acute triangle is when all the three acute angles are equal. This D is called an equiangular triangle. Figure 2.7 shows an equiangular triangle.

    Figure 2.7

    Since the sum of all the angles of a triangle is 1800, it can be said that each angle of an equiangular triangle is 600 .

  2. Obtuse triangle : A triangle in which one of the angles is obtuse is called as an obtuse triangle. Figure 2.8 shows an obtuse triangle.

    Figure 2.8

    Since the sum of all the angles of a triangle is 1800 it can be said that the other two angles of an obtuse triangle are acute.

  3. Right Triangle : It is a triangle in which one of the angles is a right angle. Figure 2.9 shows a right triangle.

    Figure 2.9

    Since Ð KJL is 900 it can be said that Ð JKJL and Ð JLK are complementary. In a right triangle the side opposite to the right angle is called the hypotenuse.

Index

2.1 Introduction
2.2 Sum Of The Angles Of A Triangle
2.3 Types of Triangles
2.4 Altitude, Median And Angle Bisector
2.5 Congruence Of Triangles
2.6 Sides Opposite Congruent Angles

Chapter 3

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