Chap 12 Triangles

Chap 12

Triangles

Some Important facts:

1.    A closed figure obtained by joining three non-collinear points is called a triangle. Symbol ‘∆’ is used to denote a triangle.

2.    A triangle has three sides, three angles and three vertices.

3.    Three sides and three angles of a triangle are called its six parts.

4.    Triangle divides the plane into three parts – interior, exterior and triangle itself.

5.    A triangle together with its interior constitutes the triangular region.

6.    The sum of three angles of a triangle is 180°.

7.    Any exterior angle of a triangle is equal to sum of its interior opposite angles.

8.    The sum of two sides of a triangle is greater than its third side.

9.    A triangle which has all the sides of different lengths is called a scalene triangle.

10. A triangle having two sides equal is called as isosceles triangle.                                    

11. A triangle having all its sides equal is called a equilateral triangle.                                                    

12. A triangle, all whose angles are acute is called an acute angled triangle.

13. A triangle, one of whose angles is a right angle, is called a right angled triangle.

14. A triangle, one of whose angles is an obtuse angle, is called an obtuse angled triangle.