# RD Sharma Solutions for Class 9 Maths Chapter 20: Surface Area and Volume of a Right Circular Cone

A Right Circular Cone is a cone in which, if we draw a straight line from the cone's apex to the circular plane of the cone, it meets at the centre of the circular plane. In our daily life, we come across many objects, which are examples of the Right Circular Cone. These include traffic cones, ice cream cones, pencil tips, birthday caps, funnels, megaphones, temple tops etc.

This chapter comprises all the properties and formulas related to a right circular cone. The properties of a Right Circular Cone are as follows:

• Suppose we draw a straight line from the apex of a Right Circular Cone to the circular surface. Then it will pass through the centre of the circular surface.
• If an isosceles triangle is rotated around its longitudinal axis, then a Right Circular Cone is formed
• The slant height of a Right Circular Cone is the line joining the cone's apex to the side edge of the circular surface, while the straight height of the cone is the length of the line joined from the apex to the centre of its circular surface.
• The longitudinal cross-section of a Right Circular Cone through its apex is an Isosceles triangle
• The lateral cross-section anywhere of a Right Circular Cone is a circle

There are 2 surface areas in a Right Circular Cone. Those are curved surface area and base area. Curved Surface Area = πRl (where R = radius of the circular surface, l = slant height of the Right Circular Cone)

Base Area = πR2 (R = Radius of the circle)

Total Surface Area = πR(R + l) square units

The formula to determine the volume of the Right Circular Cone is 