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Glencoe Math: Course 3, Volume 2

GM

Glencoe Math: Course 3, Volume 2 View details

5. Surface Area of Cones

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Exercise 1 Page 634

The lateral area of a right cone is half the product of the circumference of the base and the slant height.

$678.6 ft^{2}$

Practice makes perfect

We want to find the lateral area of the given cone.

To do so, we must know that the lateral area of a right cone is half the product of the circumference of the base and the slant height.

L . A . = \frac{1}{2} \cdot 2 π r \cdot ℓ \Leftrightarrow L . A . = π r ℓ

In this formula,

r

is the radius and

ℓ

is the slant height of the cone. With this information we are able to calculate the lateral area of the cone. To do so, we will substitute

r = 12

and

ℓ = 18

into the formula for the lateral area. Let's do it!

L . A . = π r ℓ

$r = 12$ , $ℓ = 18$

L . A . = π (12) (18)

Multiply

L . A . = π (216)

CommutativePropMult

Commutative Property of Multiplication

L . A . = 216 π

Use a calculator

L . A . = 678.584013 \dots

Round to $1$ decimal place(s)

L . A . \approx 678.6

The lateral area of the given cone, to the nearest tenth, is

678.6

square feet.

Subchapter links

Guided Practice p.634

Independent Practice p.635-636

H.O.T. Problems p.636

Extra Practice p.637

Standardized Test Practice p.638

Common Core Review p.638