What Have We Discussed ?

The six elements of a triangle are its angles and the sides.

The line segment joining a vertex of a triangle to the mid point of its opposite side is called a of the triangle.

A triangle has medians.

The perpendicular line segment from a vertex of a triangle to its opposite side is called an of the triangle.

A triangle has altitudes.

An exterior angle of a triangle is formed, when a side of a triangle is produced. At each vertex, you have ways of forming an exterior angle.

A property of exterior angles: The measure of any exterior angle of a triangle is equal to the of the measures of its interior opposite angles.

The angle sum property of a triangle: The total measure of the three angles of a triangle is °.

A triangle is said to be equilateral, if each one of its sides has length.

In an triangle, each angle has measure 60°.

A triangle is said to be , if atleast any two of its sides are of same length.

The non-equal side of an isosceles triangle is called its base; the base angles of an isosceles triangle have measure.

Property of the lengths of sides of a triangle: The sum of the lengths of any two sides of a triangle is greaterlesser than the length of the third side.

The difference between the lengths of any two sides is smallerbigger than the length of the third side. This property is useful to know if it is possible to draw a triangle when the lengths of the three sides are known.

In a right angled triangle, the side opposite to the right angle is called the and the other two sides are called its legs.

In a angled triangle, the square on the hypotenuse = the sum of the squares on its legs. If a triangle is not right-angled, this property does not hold good.

This property is useful to decide whether a given triangle is right-angled or not.