Special triangles

Two Special Triangles: Equilateral and Isosceles

A triangle in which all the three sides are of equal lengths and each angle has measure 60o is called an equilateral triangle.

In an equilateral triangle,
AB = BC = CA

And ÐA = ÐB = ÐC = 600

A triangle in which two sides are of equal lengths is called an isosceles triangle

In triangle XYZ,
XY = XZ

Sum of the Lengths of Two Sides of a Triangle
The sum of the lengths of any two sides of a triangle is greater than the length of the third side.

 

 In the above figure,
AB + BC > AC
Also, the difference between the lengths of any two sides of a triangle is smaller than the length of the third side.