Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
3. Surface Areas of Pyramids and Cones
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Exercise 16 Page 713

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

1044in^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.=1/2* 2π r* l ⇔ L.A.=π rl

In this formula, r is the radius and l is the slant height of the cone. Although we do not have the slant height, we can find it using the Pythagorean Theorem. Since the diameter of the base is 26 inches, we have that its radius is 26÷ 2=13 inches.

In this right triangle, the legs are 13 inches and 22 inches long. The hypotenuse is l. We will substitute these values in the Pythagorean Theorem and solve for l.
a^2+b^2=c^2
13^2+ 22^2= l^2
Solve for l
169+484=l ^2
653=l ^2
sqrt(653)=l
l=sqrt(653)
The hypotenuse of the right triangle, and therefore the slant height of the cone, is sqrt(653) inches long.
With this information we are able to calculate the lateral area of the cone. To do so, we will substitute r=13 and l=sqrt(653) into the formula for the lateral area. Let's do it!
L.A.=π rl
L.A.=π ( 13)( sqrt(653))
L.A.=1043.637836...
L.A.≈ 1044
The lateral area of the given cone, to the nearest whole number, is 1044 square inches.