Theory:

Let's learn the types of triangle:
Triangles can be classified based on its sides as well as its angles.
Types of triangles based on its side lengths are as follows.
  • Equilateral triangle
  • Isosceles triangle
  • Scalene triangle
 A triangle is an equilateral when all its sides are equal in length.
 Theory3.1.png
Example:
Theory3.2.png
 
In here, the sides are equal in measure \(AB=BC=CA=5\) units.
A triangle is isosceles when two of its sides are equal in length.
Theory3.3.png
Example:
Theory3.4.png
 
In here, the two of the sides are equal in measure \(AB=CA=1\) unit and \(BC=√2\) units.
A  triangle is a scalene when all the three sides are unequal.
Theory3.5.png
Example:
Theory3.6.png
 
In here, all the sides are unequal in measure \(AB=7.7, CA=5\) units and \(BC=9\) units.
Types of triangles based on its angles are as follows.
  • Acute angled triangle
  • Right angle triangle
  • Obtuse angled triangle
A triangle is acute angle triangle when all the three of its angle are acute (less than 90°).
Theory3.7.png
Example:
Theory3.8.png
 
In here, all the three angles are less than \(90°\).  That is, \(∠A=60°, ∠B=50°\) and \(∠C=70°\).
A triangle is right angle triangle when one of its angles is a right angle (90°), and the other two are acute angles (less than 90°).
Theory3.9.svg
Example:
Theory3.10.png
 
In here, one among the angle is \(90°\), and the other two are acute. That is, \(∠A=40°, ∠B=50°\) and \(∠C=90°\).
A  triangle is an obtuse angle triangle when one of its angles is an obtuse angle (greater than 90°), and the other two are acute angle (less than 90°).
Theory3.11.png
Example:
Theory3.12.png
 
In here, one among the angle greater than \(90°\) and the other two are acute. That is, \(∠A=120°, ∠B=35°\) and \(∠C=25°\).