Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
Chapter Review
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Exercise 31 Page 660

Use the formulas for the surface area and volume of a cone.

Surface Area: ≈ 439.82 m^2
Volume: ≈ 562.10 m^3

Practice makes perfect

The given solid is a cone with a radius of 7 and a slant height of 13. Let's first calculate the surface area and then the volume.

Surface Area

To calculate the surface area of a cone, we can use the known formula where r is the radius of the base and l is the slant height of the cone. S=Ï€ rl+Ï€ r^2By substituting 7 for r and 13 for l into the formula, we can calculate S.

S=Ï€ rl+Ï€ r^2
S=Ï€( 7)( 13)+Ï€( 7)^2
â–¼
Simplify right-hand side
S=Ï€(7)( 13)+49Ï€
S=91Ï€+49Ï€
S=140Ï€
S=439.82297...
S≈ 439.82

The surface area of the cone is about 439.82 square meters.

Volume

To calculate the volume of a cone, we can use the following formula. V= 13Ï€ r^2 h Here, r is the radius and h is the height of the cone. We are given the radius of the cone but missing the height of the cone. From the figure, we can see a right triangle formed by the radius, the slant height, and the height of the cone.

We can use the Pythagorean Theorem to find the length of the longer leg of the triangle. Let's set c=13 and b= 7 and substitute these values in the Pythagorean formula.

c=a^2+b^2
13^2=a^2+ 7^2
â–¼
Solve for a
169=a^2+49
120=a^2
± sqrt(120)=a
a=± sqrt(120)

We only need the positive value of the square root because height is a distance. Therefore, we have a cone with a height of sqrt(120) meters.

By substituting 7 for r and sqrt(120) for h into the formula, we can calculate V.

V=1/3Ï€ r^2 h
V=1/3Ï€ ( 7)^2 ( sqrt(120))
â–¼
Simplify right-hand side
V=1/3Ï€(49)(sqrt(120))
V=1/349sqrt(120) π
V=49sqrt(120) π/3
V=562.10224...
V≈ 562.10

The volume of the cone is about 562.10 cubic meters.