Triangle: We just studied polygons. Triangle is a polygon with three sides. So, we could define a triangle as a plane closed figure bounded by three line segments.
A triangle is a polygon with three edges and three vertices. It is one of the most basic shapes in geometry. A triangle with vertices A, B, and C is denoted by ∆ABC.
Kind of Triangles
Classification of triangles based on the length of the sides
Scalene Triangle | A triangle in which all three sides are of different lengths is called Scalene Triangle.
In this type of triangle: |
![]() |
Isosceles Triangle | A triangle in which two sides are of the same length is called Isosceles Triangle
In this type of triangle: |
![]() |
Equilateral Triangle | A triangle in which all three sides are of the same length is called Equilateral Triangle.
In this type of triangle: |
![]() |
Some of the diagrams have been adopted from https://en.wikipedia.org/wiki/Triangle
Classification of Triangles based on the angles
Acute-angled Triangle | A triangle in which all the three angles are more than |
![]() |
Right-angles Triangle | A triangle in which one of the angles is |
![]() |
Obtuse-angled triangle | A triangle in which one of the angles is more than |
![]() |
Some of the diagrams have been adopted from https://en.wikipedia.org/wiki/Triangle
Term related to a Triangle
Median | A line segment joining the vertex to the mid-point of the opposite side of a triangle is called median.
In this vertex
|
![]() |
Centroid | The point of intersection of three medians is called centroid. |
|
Altitude | The perpendicular drawn from the vertex to the opposite side.
Here |
![]() |
Orthocenter | The intersection of the three altitudes is called the Orthocenter of the triangle.
Here |
![]() |
Angle Bisector | A line segment that bisects and interior angle of a triangle is called angle bisector.
Here |
![]() |
Incentre and Incircle | The point of intersection of internal angle bisectors is called the Incentre.
Now if you draw a circle with the center
|
![]() |
Perpendicular Bisector or Right Bisector | A line bisecting any side of the triangle and perpendicular to it is called perpendicular bisector of that side of the triangle.
Here BC is being bisected by |
![]() |
Circumcenter and Circumcircle | The point of intersection of the perpendicular bisectors of the sides of the triangle is called Circumcenter.
Here |
![]() |
Exterior Angle and Interior Opposite Angles of a Triangle | ![]() |
Some of the diagrams have been adopted from https://en.wikipedia.org/wiki/Triangle