To know more about triangles To know the classifications of triangles

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3. Triangles
A triangle is a 3-sided closed figure. It has three vertices(or
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. 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 are equal
is called an isosceles triangle.
c) Scalene triangle:
A triangle whose all sides are
different is called a scalene triangle.

6. 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. Triangle-Based on Angles
c) Right triangle:
A triangle whose one angle is exactly 90˚ is called right
triangle or right angle triangle.

8. Examples
Based on Angles
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 Sides
a) 6cm,3cm,5cm –
Scalene triangle
b) 6cm,6cm,6cm-
Equilateral triangle
c) 7cm,7cm,5cm-
Isosceles triangle
d) 3cm,4cm,5cm- Scalene
triangle

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