Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
5. Volumes of Pyramids and Cones
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Exercise 14 Page 730

Use the formula for the volume of a pyramid.

562.9 ft^3

Practice makes perfect

Let's take a look at the given square pyramid.

Orange square pyramid. Sides of the base are blue and have blue labels '11 ft'. Height of one of the triangular sides is green and is labeled '15 ft'
To calculate the volume of a pyramid, we can use a known formula where B is the area of the base and h is the height. V=1/3Bh

The base of the pyramid is a square with the side length of 11ft. Let's calculate its area! B = s^2 ⇒ B = 11^2 B= 121ft^2 We are given that the slant height l is 15ft. Now let's focus on the right triangle created within the pyramid.

square pyramid

The slant height of the pyramid is the hypotenuse of the triangle. The legs of the triangle are the height of the pyramid h and half of the side length of the pyramid.

Notice that we can find the height of the pyramid using the Pythagorean Theorem.
(11/2)^2+h^2= 15^2
Solve for h
5.5^2+h^2=15^2
30.25+h^2=225
h^2=194.75
h=sqrt(194.75)
Note that, when solving the above equation, we only needed to consider the principal root because h is a positive number. Finally let's substitute the base area and the height of the pyramid into the formula and calculate V.
V=1/3Bh
V=1/3( 121)( sqrt(194.75))
Simplify right-hand side
V=1/3(121sqrt(194.75))
V=121sqrt(194.75)/3
V=562.863191...
V≈ 562.9
The volume of the pyramid is approximately 562.9 cubic feet.