Key learning points

1. The slanted surface of a cone can be cut into congruent triangles.
2. These form a parallelogram with dimensions of the slanted length and half of the circumference of the base.
3. The area of the slanted surface can be written as πrl
4. The surface area of the cone is therefore πrl + πr^2
5. The slanted length can be calculated from the height of the cone and radius of the base

Keywords

• Cone - A circular cone is a 3D shape that has a circular base and one curved surface that narrows from the base to a fixed point called the apex/vertex.

• Right cone - A line drawn through the apex and centre of the base of a right circular cone will be perpendicular to the base.

• Apex - The apex is the point (vertex) which is the greatest perpendicular distance from the base.

Common misconception