 Hello and welcome to the session, I am Deepika here. Let's discuss the question which says, rewrite the formula for the volume of the frustum of a cone given to us in section 13.5 using the symbols as explained. In the section 13.5, there was a removal of a smaller right circular cone by cutting the given cone by a plane parallel to its base. So let's start the solution. Now we are using the figure of the previous question. Let V be the volume of the frustum of a cone. Then V is equal to volume of cone VAB minus volume of cone VA dash P dash. So this implies V is equal to, now we know that volume of cone is 1 by 3 pi r square h. Therefore volume of cone VAB is 1 by 3 pi r1 square into h1 minus volume of cone VA dash V dash is 1 by 3 pi r2 square into h1 minus h. This implies V is equal to, let us take pi by 3 common, we have h1 r1 square minus h1 minus h r2 square. This implies V is equal to pi by 3 into, now in the previous question we have solved h1 is equal to h r1 upon r1 minus r2 into r1 square minus, similarly we have solved h1 minus h is h r2 upon r1 minus r2 into r2 square because h1 is equal to h r1 upon r1 minus r2 and h1 minus h is equal to h r2 upon r1 minus r2. And this implies V is equal to pi by 3 into h r1 cube upon r1 minus r2 minus h r2 cube upon r1 minus r2. So this implies V is equal to pi by 3, let us take h upon r1 minus r2 common, so we have r1 cube minus r2 cube. So this implies V is equal to pi by 3 into h upon r1 minus r2 into r1 minus r2 into r1 square plus r1 r2 plus r2 square because a cube minus b cube is equal to a minus b into a square plus a b plus b square. This implies V is equal to 1 by 3 pi h into r1 square plus r1 r2 plus r2 square thus we have derived the formula for volume of a, first term of a cone this is equal to 1 by 3 pi h into r1 square plus r2 square plus r1 r2. I hope the solution is clear to you, bye and take care.