# NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.7 – Part 3

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Q-6 The volume of a right circular cone is. If the diameter of the base is, find

Height of the cone

Slant height of the cone

Curved surface area of the cone

Solution:

I. Diameter of the base of the cone

Therefore radius ()

Let the height of the cone be

Now, volume of the cone =

II. Radius , Height , Let the slant height of the cone be , than

III. Given,

Radius

Slant height

Therefore curved surface area

Q-7 A right triangle with sides , and is revolved about the side. Find the volume of the solid so obtained.

Solution:

Note than when right triangle is revolved we get a cone with the same radius as the base of the right triangle.

Height is.

In triangle

Base is

Height is.

Cone so obtained has radius r = 5 cm and height 12 cm. Its volume,