 Hi and welcome to the session. Today we will learn about triangle and its properties. First of all, let us learn about equilateral triangle. Equilateral triangle is a triangle in which all the sides are of equal length. For example, here in triangle ABC all the sides are equal to 5 cm. That means all the sides are equal to each other. So here triangle ABC is an equilateral triangle. Now there is an important point which you need to remember about an equilateral triangle that is all the angles are equal to 60 degrees. That means in an equilateral triangle all the sides are equal and all the angles are equal to 60 degrees each. That means all the angles are equal to each other. Now let's move on to isosceles triangle. Isosceles triangle is a triangle in which two sides are of equal length. For example, here in triangle PQR side PQ and side PR are of length 2.9 cm and side QR is of length 4 cm. That means side PQ is equal to side PR. Now here two sides are of equal length that is 2.9 cm. That means here triangle PQR is an isosceles triangle. Now the non-equal side of the isosceles triangle is known as the base and the angles which are opposite to equal sides are known as base angles. Now we have in an equilateral triangle the base angles opposite to equal sides are equal. So here angle Q will be equal to angle R as angle Q is opposite to side PR and angle R is opposite to side PQ. And these two sides are equal sides. Let's take an example. Here in triangle ABC side AB is equal to side AC and angle B is equal to 50 degrees. And we need to find the measure of angle C and angle A. Now in this triangle side AB is equal to side AC that means triangle ABC is an isosceles triangle. And the angles opposite to equal sides are equal. So that means angle B will be equal to angle C as they are opposite to equal sides AB and AC. So angle C will be equal to 50 degrees because angle B is equal to angle C. Now we need to find the measure of angle A. So here by angle some property we know that angle A plus angle B plus angle C will be equal to 180 degrees. That means angle A will be 180 degrees minus 50 degrees minus 50 degrees which will be equal to 80 degrees. That means measure of angle A is equal to 80 degrees. Now let's move on to our next topic. Some of the lengths of two sides of a triangle. Consider the triangle PQR in this side PQ is equal to 6.2 centimeters, side QR is equal to 5.6 centimeters and side RP is equal to 7 centimeters. Here 6.2 centimeters plus 5.6 centimeters is greater than 7 centimeters. So that means we have PQ plus QR is greater than PR. Also 5.6 centimeters plus 7 centimeters will be greater than 6.2 centimeters. So that means QR plus RP will be greater than PQ. Also 7 centimeters plus 6.2 centimeters will be greater than 5.6 centimeters. So we have RP plus PQ will be greater than QR. So from this we conclude that the sum of the lengths of any two sides of a triangle is greater than the third side. Similarly we can notice that 6.2 centimeters minus 5.6 centimeters will be less than 7 centimeters. So we have PQ minus QR will be less than PR 7 centimeters minus 5.6 centimeters will be less than 6.2 centimeters. So that means PR minus QR will be less than PQ. Also 7 centimeters minus 6.2 centimeters will be less than 5.6 centimeters. That is PR minus PQ will be less than QR. So this implies that the difference between the length of any two sides of a triangle is smaller than the length of the third side. With this we finish this session. Hope you must have understood all the concepts. Goodbye, take care and have a nice day.