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 14 Page 713

The lateral area of a regular pyramid is half the product of the perimeter of the base and the slant height of the pyramid.

51m^2

Practice makes perfect

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

We know that the lateral area of a regular pyramid is half the product of the perimeter p of the base and the slant height l of the pyramid. L.A.=1/2pl

Although we are not given the slant height of our pyramid, we can find it by using the Pythagorean Theorem. Note that the base of our triangle will be 4 ÷ 2 = 2 meters.

In this right triangle, the legs are 6 and 2 meters long. The hypotenuse is l. We will substitute these values into the Pythagorean Theorem and solve for l.
a^2+b^2=c^2
6^2+ 2^2= l^2
Solve for l
36+4=l ^2
40=l ^2
sqrt(40)=l
l=sqrt(40)
l=sqrt(4 * 10)
l=sqrt(4)* sqrt(10)
l=2sqrt(10)
The hypotenuse of the right triangle, and therefore the slant height of the pyramid, is 2sqrt(10) meters long.
The base of the pyramid is a square with the side length of 4m. Let's calculate its perimeter! p=4s ⇒ p=4( 4)=16m With this information, we are now able to calculate the lateral area of the pyramid. We will substitute p=16 and l=2sqrt(10) into the formula for lateral area. Let's do it!
L.A.=1/2pl
L.A.=1/2( 16)( 2sqrt(10))
Evaluate right-hand side
L.A.=16/2(2sqrt(10))
L.A.=8(2sqrt(10))
L.A.=50.596442...
L.A.≈51
The lateral area of the given pyramid is about 51 square meters.