Triangles and Quadrilaterals

definition of triangle and classification of triangles with examples

1. By , Jeenath Kamila ( [email protected] )

2. Unit - 13 Triangles and Quadrilaterals [email protected]

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 Δ ABC, A,B,C are vertices, A̅B̅, B̅C̅ 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.

4. 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.

5. 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 .

6. 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.

7. 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

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