definition of triangle and classification of triangles with examples

1. By ,
Jeenath Kamila
( kamilaa1985@gmail.com )

2. Unit - 13
Triangles and
Quadrilaterals
kamilaa1985@gmail.com

3. Triangles
• A triangle is a 3-sided closed figure. It has three
vertices(corners) and three sides. The sum of the angles is
always 180˚.
In ΔABC,
• A,B,C are vertices, A̅B̅ , B̅ C̅ and A̅C̅ are sides. AB is the base of
ΔABC. ˂C opposite to the base AB is called vertical angle to the
base ˂A and ˂B are called base angles.

5. Classifications of Triangle-
Based on Sides
a) Equilateral triangle:
A triangle having all its three sides
are equal is called equilateral
triangle
b) Isosceles triangle:
A triangle with two sides equal is
called an isosceles triangle.
c) Scalene triangle:
A triangle whose all sides are
different is called a scalene triangle.

6. Classifications of Triangle-
Based on Angles
a) Acute triangle:
A triangle which has the angles
are less than 90˚ is called acute
triangle or acute angle triangle.
b) Obtuse triangle:
A triangle whose one angle is
more than 90˚ and less than 180˚
is called obtuse triangle or obtuse
angle triangle .

7. Classifications of Triangle-
Based on Angles
c) Right triangle:
A triangle whose one angle is right ( 90˚) is called right
triangle or right angle triangle.

8. Examples
Based on Sides
a) 90˚, 45˚, 45˚ - Right
triangle
b) 60˚, 60˚, 60˚- Acute
triangle
c) 130˚, 40˚, 10˚- Obtuse
triangle
d) 80˚, 60˚, 40˚ - Acute
triangle
Examples
Based on Angles
a) 6cm,3cm,5cm –
Scalene triangle
b) 6cm,6cm,6cm-
Equilateral triangle
c) 7cm,7cm,5cm-
Isosceles triangle
d) 3cm,4cm,5cm-
Scalene triangle

9. kamilaa1985@gmail.com