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December 18, 2014

December 18, 2014

Posted by **tmouery** on Saturday, March 9, 2013 at 8:16pm.

I tried doing this using the formula shown in my book, but it came out wrong. the formula I was using was for a triangular prism. What the heck is the formula for a pentagonal prism?

- geometry -
**Ms. Sue**, Saturday, March 9, 2013 at 8:23pmhttp://mathworld.wolfram.com/PentagonalPrism.html

http://easycalculation.com/area/learn-penta-prism.php

- geometry -
**Reiny**, Saturday, March 9, 2013 at 8:31pmtriangular prism ---> base is a triangle

pentagonal prism ---> base is a pentagon

So clearly you can't use the triangular prism formula for this question , but you an generalize it looking what it describes.

I don't know what they gave you, but the surface area of a triangular prism consists of

2 congruent triangular bases + 3 congruent rectangles

so the surface area of a pentagon

= 2 (area of the pentagon) + 5rectangles

you are given that the perimeter is 20, so each side of the base is 20/5 = 4, and the height is 10

so the surface area of the 5 rectangles is 5(4)(10) = 200

add the 2 pentagon areas of 32 each for a total of

200 + 64 = 264 cm^2

your text should give you the definitions of lateral and total surface areas, make the necessary adjustments.

- geometry -
**tmouery**, Saturday, March 9, 2013 at 9:23pmThank you, that makes more sense than what I tried.

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