Notes On Cone - CBSE Class 9 Maths

A cone is a solid figure with a circular base that tapers to a point called the vertex. It is said to be a right circular cone if the line joining the vertex of a cone to the centre of its base is at right angle to the radius of the base.

Let 'r' be the base radius, 'h' be the height, 'l' be the slant height of a right circular cone. Slant height, radius and the height of a cone forms a right angled triangle. Then by applying Pythagoras theorem l =  r 2 + h 2 .

Base area of the cone = πr2

Curved surface area of the cone = πrl

Total surface area of the cone = πrl + πr2 = πr(l + r)

Volume of the cone = 1 3 πr2h

Summary

A cone is a solid figure with a circular base that tapers to a point called the vertex. It is said to be a right circular cone if the line joining the vertex of a cone to the centre of its base is at right angle to the radius of the base.

Let 'r' be the base radius, 'h' be the height, 'l' be the slant height of a right circular cone. Slant height, radius and the height of a cone forms a right angled triangle. Then by applying Pythagoras theorem l =  r 2 + h 2 .

Base area of the cone = πr2

Curved surface area of the cone = πrl

Total surface area of the cone = πrl + πr2 = πr(l + r)

Volume of the cone = 1 3 πr2h

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