What is a triangle?
A simple closed curve or a polygon formed by three line-segments (sides) is called a triangle.
The above shown shapes are triangles. The symbol of a triangle is ∆.
A triangle has
There are six types of triangles, 3 with respect to sides and 3 with respect to angles.
Three types of triangle with respect to sides
(i) A triangle having all the three line-segments or sides unequal is called a scalene triangle.
(ii) A triangle having a pair of its sides or two line-segments equal is called an isosceles triangle.
Here AB = AC.
(iii) A triangle having all the three line-segments or sides equal is called an equilateral triangle.
Here AB = BC = CA.
Types of triangle with respect to angles
(i) A triangle in which all the three angles are acute is called an acute angled triangle.
∠ABC, ∠ACB and ∠BAC are all acute angles.
Acute Angled Triangle
(ii) A triangle in which one of the three angles is a right angle is called a right angled triangle.
∠ABC = one right angle.
Right Angled Triangle
(iii) A triangle where one of the three angles is more than a right angle (or is an obtuse angle) is called an obtuse angled triangle.
∠ABC is an obtuse angle.
Obtuse Angled Triangle
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Related Concepts on Geometry - Simple Shapes & Circle