Big Ideas Math Geometry, 2014
BI
Big Ideas Math Geometry, 2014 View details
6. Volumes of Pyramids
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Exercise 21 Page 640

Practice makes perfect
a Let's begin by drawing the given pyramid.
The volume of the pyramid above is one-third the area of the base multiplied by the height. V = 1/3(6* 6)8 = 96 ft^3 Next, let's double the height of the pyramid and find its volume. The height of the new pyramid is 16 feet.
V = 1/3Bh
V_2 = 1/3( 6* 6) 16
V_2 = 192
The volume of the second pyramid is 192 ft^3, which is the same as 2* 96 ft^3. The volume of the second pyramid is twice the volume of the first one.

If the height of a pyramid with a square base is doubled, then the volume is also doubled.

b From Part A we know the volume of the original pyramid is 96 ft^3. In this part, let's keep the original height but double the side length of the base.
As we can see, the new side length of the base is 12 ft. Let's proceed to find its volume.
V = 1/3Bh
V = 1/3( 12* 12) 8
V = 384
The volume of the new pyramid is 384 ft^3, which can be rewritten as 4* 96 ft^3. Thus, the volume of the new pyramid is four times the volume of the original one.

If the side length of the square base of a pyramid is doubled, then the volume is quadrupled.

c In this part, let's consider a pyramid with a square base with side length of x and height h.
The volume of the pyramid above is given by V= 13x^2h. Next, let's find the volume of a second pyramid with the same base but its height is 2h.
V_2 = 1/3Bh
V_2 = 1/3 x^2* 2h
â–Ľ
Simplify right-hand side
V_2 = 2(1/3x^2h)
V_2 = 2 V_1
As we can see, the volume of the pyramid doubled. Now, let's find the volume of a third pyramid with height h and side length of the base 2x.
V_3 = 1/3Bh
V_3 = 1/3 (2x)^2h
â–Ľ
Simplify right-hand side
V_3 = 1/3* 4x^2h
V_3 = 4(1/3x^2h)
V_3 = 4 V_1
Thus, if we double the side length of the base, the volume quadruples. In conclusion, the answers to Parts A and B are true for any square pyramid.