Theory:

A closed figure with three sides is a triangle.
 
We may classify triangles based on their sides and angles.
 
Let us look at each one of them in detail.
The naming of triangles based on sides
Type 1: Equilateral triangle
 
A triangle with all three equal sides is an equilateral triangle.
 
24.svg
 
Here, \(\overline{AB} = \overline{BC} = \overline{AC}\).
 
In other words, all sides of triangle \(ABC\) are equal.
 
Type 2: Isosceles triangle
 
A triangle with two equal sides and a third unequal side is an isosceles triangle.
 
25.svg
 
Here, \(\overline{AB} = \overline{AC}\)
 
Two sides of the triangle \(ABC\) are equal while the third side is unequal.
 
Type 3: Scalene triangle
 
A triangle with all three unequal sides is a scalene triangle.
 
26.svg
 
Here, the three sides \(AB\), \(BC\) and \(AC\) are unequal.
The naming triangles based on angles
Type 1: Acute angled triangle
 
If all three angles in a triangle are acute, then it is an acute angled triangle.
 
Type 2: Right angled triangle
 
If one of the angles of the triangle is 90^circ, then it is a right angled triangle.
 
Type 3: Obtuse angled triangle
 
If any one of the angles is obtuse, then it is an obtuse angled triangle.