Page 1 - Lesson Notes-Ch.13 SA and Volumes(Cone)
P. 1
SAI International School
CLASS - IX
Mathematics
CHAPTER-13: SURFACE AREAS AND VOLUMES
Lesson Note-3 [CONE]
Right Circular Cone
If we revolve a right-angled triangle about one of its sides by taking other as its axis
then the solid shape so formed is known as a Right Circular Cone. It has only two
surface areas, one lateral or Curved surface and the other is the circular base.
A cone does not have uniform (or congruent) cross-sections.
Where,
r is the radius
h is the vertical height (height) .
l is the slant height.
Slant height ( ) = √ℎ +
2
2
Surface of a Right Circular Cone
2
1. Area of base = πr sq. unit
2. Curved Surface Area (CSA)= = √ + ℎ sq. unit
2
2
3. Total Surface Area = Area of base + CSA = +
2
= ( + ) sq. unit
1
