1. TRIANGLES
We have already learnt that a three sided (line segments) closed plane figure is called a triangle. When the three sides of a triangles meet, they also form three angles. So it is called a triangle.

2. Different Types of Triangles
There are several different types of triangles.
You can classify a triangle by its sides and its angles.
There are THREE different classifications for triangles based on their sides.
There are three different classifications for triangles based on their angles.

3. Classification of Triangles based on Sides
Equilateral Triangle:
If all the three sides of a triangle are equal then it is called an Equilateral triangle.
Isosceles Triangle:
If any two sides of a triangle are equal then it is called an isosceles triangle.

4. Scalene Triangle: Example
If all the three sides of a triangle are unequal then it is called a scalene triangle
Example
Q1:- Write the type of triangle, based on their sides
Ans:
In ∆ABC, AB=7cm, BC=7cm, CA=7cm. All sides in the triangle are equal. So, ∆ABC is an equilateral triangle.

5. Q2:- Write the type of triangle, based on their sides
Ans:-
In ∆PQR, PQ=5cm, QR=2cm, RP=2cm. Two sides PQ and RP in the triangle are equal. So, therefore ∆PQR is an isosceles triangle.
Q3:- Write the type of triangle, based on their sides
Ans:-
In ∆XYZ, XY=7cm, YZ=5cm , ZX=4cm. All three sides in the triangle are unequal. So, ∆ABC is an scalene triangle.

6. Q4:- Write the type of triangle, based on their sides
In ∆ABC, AB=3cm, BC=6cm, CA=3cm.
Ans:-
Two sides AB and CA in the triangle are equal. So, ∆ABC is an isosceles triangle.
Q5:- Write the type of triangle, based on their sides
In ∆PQR, PQ=4cm, QR=4cm, RP=4cm.
All sides in the triangle are equal. So, ∆PQR is an equilateral triangle.
Q6:- Write the type of triangle, based on their sides
In ∆XYZ, XY=4cm, YZ=3cm, ZA=6cm.
All three sides in the triangle are unequal. So, ∆XYX is an scalene triangle.