Triangle

Definition

In geometry, a triangle is a plane figure that is enclosed by three line segments.

Parts

• Side
• Angle
• Vertex

Properties

1. The sum of all the angles of a triangle is equal to 180°
2. The sum of the lengths of any two sides of a triangle is greater than the length of the third side
3. The difference between any two sides of a triangle is less than the length of the third side
4. An exterior angle of a triangle is equal to the sum of its interior opposite angles. This is called the exterior angle property of the triangle

Formulas

Area of a Triangle

It is the total space enclosed by the triangle. The formula is given below:

Perimeter of a Triangle

It is the distance covered around the edges of a triangle or simply the length of the boundary covered. The formula is given below:

Types

Triangles are classified into two groups: based on sides, 1) scalene, 2) isosceles, and 3) equilateral triangles; based on angles, 1) acute angle, 2) obtuse angle, and 3) right or right-angled triangles.

The differences between the types are given below:

Apart from the above three types, there is Equiangular Triangle with all three internal angles equal to 60° and, thus having all sides equal, similar to an Equilateral Triangle

• Triangle Worksheets
  • Congruent Triangles Worksheets
  • Special Right Triangles Worksheets
  • Special Triangles Worksheets
  • Similar Triangles Worksheets
  • Area of a Triangle Worksheets
  • Area of Triangles and Parallelograms Worksheets
  • Area of Triangles and Trapezoids Worksheets
  • Area and Perimeter of Triangles Worksheets
  • Angles in a Triangle Worksheets
  • Classifying Triangles Worksheets
  • Isosceles and Equilateral Triangles Worksheets
  • Right Triangle Worksheets
  • Right Triangle Trigonometry Worksheets
  • Triangle Sum Theorem Worksheets
  • Midsegment of a Triangle Worksheets
  • Triangle Inequality Theorem Worksheets
  • Special Segments in Triangles Worksheets
  • Triangle Proportionality Theorem Worksheets
  • Centers of Triangles Worksheets
  • Constructing Triangles Worksheets

• Further Reading
  • Scalene Triangle
  • Isosceles Triangle
  • Equilateral Triangle
  • Acute angled Triangle
  • Obtuse angled Triangle
  • Right triangle Triangle
  • Special Right Triangles 
  • Congruent Triangles
  • Altitude of a Triangle
  • Similar Triangles
  • Median of a Triangle
  • Triangle Inequality Theorem
  • Centroid of a Triangle
  • Triangle Sum Theorem
  • Incenter of a Triangle
  • Vertices of a Triangle
  • Hypotenuse of a Triangle
  • Isosceles Triangle Theorem
  • Exterior Angle of a Triangle
  • Midsegment of a Triangle
  • Base of a Triangle
  • Perpendicular Bisector of a Triangle
  • Angle Bisector of a Triangle