6. The Triangle and its Properties

Important concepts:

1. A triangle has three angles & three sides.

2. Median is a line segment from a vertex of a triangle to the mid-point of its opposite side.

3. Altitude is the perpendicular line segment from a vertex of a triangle to its opposite side.

4. Exterior angle property: Exterior angle = sum of measure of interior opposite angles.

5. Angle sum property: Measure of all angles of a triangle = 180^o

6. Equilateral triangle: all sides equal & all angles = 60^o

7. Isosceles triangle: two sides are equal & base angles are equal.

8. Property of the sides of a triangle:

• Sum of the lengths of any two sides > The length of the third side.
• Difference between the lengths of any two sides < The length of the third side.

9. Right angled triangle: Side opposite to right angle is hypotenuse.

10. Pythagoras property: Hypotenuse² = Side² + Side²