 Hi and welcome to the session. I'm Kanika and I'm going to help you to solve the following question. The question says the diameter of the base of coal is 10.5 centimeters and its land height is 10.8 meters. Find its curve surface area. Before solving this question, we should know that what is meant by a right circular coal. The solid generated by the rotation of a right angled triangle about one of the sides containing the right angle is called a right circular cone. So if we have right angled triangle at A and if we generate this triangle about OA then it generates a cone like this. OA is called the vertex of the core and you can see that base of this cone is circular. Radius of this cone is AB. Length OA is called the height of the core and this that is OB is known as land height of the core. So we usually denote height by edge, land height by L and radius by R. Now we should know the formula for finding the curve surface area of a cone. Curve surface area of a cone is equal to pi RL where R is the radius of the cone and L is the slant height of the cone. And remember that L squared is equal to H squared plus R squared. So in the order of this is the key idea in this question. Now begin with the solution. In the question we are given that diameter of the base of the cone is 10.5 centimeter. This means this whole portion is equal to 10.5 centimeters. Our diameter is equal to 10.5 centimeters therefore radius is equal to 10.5 by 2 centimeters and this is equal to 105 by 20 centimeters. It is given to us that its slant height is 10 centimeters. This is given as 10 centimeters. Now we have to determine the curve surface area of this cone. We know that curve surface area is equal to pi RL. So substitute the value of pi R and L in this. Pi is equal to 22 by 7. R is equal to 105 by 20 centimeters. L is equal to 10 centimeters. On cancelling 105 by 7 we get 50. On cancelling 10 by 20 we get 1 by 2. And on cancelling 22 by 2 we get 11. Now 11 into 15 is 165. So curve surface area of a cone is 165 centimeters square. Hence our required answer is 165 centimeters square. I hope you understood the question and enjoy the session. Bye and take care.