• The sum of the length of the two sides of a triangle is greater than the length of the third side.
• The exterior angle of a triangle is always equal to the sum of the interior opposite angles. This property of a triangle is called an exterior angle property.
• Two triangles are said to be similar if their corresponding angles of both triangles are congruent and lengths of their sides are proportional.
• Area of a triangle = ½ × Base × Height
• The sum of all the angles of a triangle (of all types) is equal to 180°.
• The perimeter of a triangle = sum of all its three sides
