McGraw Hill Glencoe Geometry, 2012
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McGraw Hill Glencoe Geometry, 2012 View details
5. Volumes of Pyramids and Cones
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Exercise 8 Page 876

Use the formula for the volume of a cone.

4712.4m^3

Practice makes perfect

To calculate the volume of a cone, we can use the following formula, where r is a radius and h is a height. V= 13π r^2 h In our exercise we are given that the slant height of a cone is 25 meters and a radius is 15 meters.

Now notice that a slant height, radius and a height h form a right triangle. Let's focus on this triangle for a little bit.

As we can see, to calculate the height of the cone, we can use the Pythagorean Theorem. Let's write an equation according to this theorem. h^2+15^2=25^2 Now let's solve this equation for h.
h^2+15^2=25^2
Solve for h
h^2+225=625
h^2=400
h=20
Note that, when solving the above equation, we only needed to consider the principal root because h is a positive number. We are given that the radius is 15m and we found that the height of the cone is 20m. Let's substitute these values into the volume formula.
V=1/3π r^2 h
V=1/3π ( 15)^2 ( 20)
Simplify right-hand side
V=1/3π(225)(20)
V=1/3(225)(20)π
V=4500/3π
V=1500π
V=4712.3889...
V≈ 4712.4
The volume of the cone is approximately 4712.4m^3.