Triangle

A triangle is a closed figure made of three line segments.

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In this figure AB, BC and CA form a closed figure. This is ΔABC.

Here AB, BC and CA are the three sides of a triangle. The point where any two sides of a triangle intersect is called the vertex of the triangle. In this figure A, B, C are the vertices.

Also when two line segments intersect they form an angle at that point. Here AB and BC intersect at B and hence forming an angle ABC. Similarly angle BCA and angle ACB.

A triangle has three vertices, three sides and also three angles. In a triangle the sum of the angles is 180°.

Different types of triangles

Triangles can be classified into different categories according to the length of the sides or the magnitude of the angles.

Based on the length of the sides it can be classified into three.

They are Equilateral triangle, isosceles triangle and scalene triangle.

• Equilateral triangle : when all the three sides of a triangle are equal in length it is called equilateral triangle
• Isosceles triangle : When two sides of a triangle are equal in length, then it is called isosceles triangle.
• Scalene triangle : A triangle having no two side equal is called scalene triangle. That is all the three sides are different in length.

Based on the magnitude of the angle it is again classified into three.

• Acute angled triangle : If each of the angles of a triangle are acute, then it is called an acute angled triangle.
• Right angled triangle : If one angle of a triangle is 90° then triangle is called right triangle.
• Obtuse angled triangle : When one of the angles of a triangle is obtuse, it is called an obtuse triangle.