McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
2. Surface Areas of Prisms and Cylinders
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Exercise 44 Page 820

Write the perimeter of the triangle in terms of the side length of the square, and use the formula to find the lateral area of a right prism.

The lateral area of the square based prism is 4sh and is greater than the lateral area of the triangular prism which is 2sqrt(3)sh.

Practice makes perfect

Let's begin by drawing the bases of the two described prisms.

Next, let's rewrite x in terms of s. To do that, we use the fact that the altitude of the triangle divides it into two 30^(∘)-60^(∘)-90^(∘) triangles.

Let's solve the relation above for x.
s = 1/2x* sqrt(3)
2sqrt(3)s = x * 3
Solve for x
2sqrt(3)s/3 = x
x = 2sqrt(3)s/3
The lateral area of a right prism equals the perimeter of the base multiplied by the height of the prism. Let h be the height of both prisms. L_(P_1) = P_(□)* h and L_(P_2) = P_(△)* h The perimeter of the square equals 4 s and the perimeter of the triangle is 3 x. L_(P_1) = 4 s h and L_(P_2) = 3 x h Let's substitute x = 2sqrt(3) s3 into the lateral area above. L_(P_1) = 4 s h and L_(P_2) = 3* 2sqrt(3) s3 * h By simplifying the right-hand side of the equation, we will obtain both lateral areas in terms of the same variables. L_(P_1) = 4 s h and L_(P_2) = 2sqrt(3) s h Since 4> 2sqrt(3), we conclude that the lateral area of the square based prism is greater than the lateral area of the triangular prism. L_(P_1) > L_(P_2)

Sketching the Prisms

Below we sketch each of the prisms used before.