ShmoopTube

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Here's your shmoop du jour.

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What is the surface area of a rigid circular cone with diameter = 10 and height = 12?

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And here are the potential answers...

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Okay, it's yet another formula trivia contest.

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So the formula is....

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surface area equals pi times r times the square root of the quantity radius squared plus height squared.

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Well, they give us the height. Now we need the diameter to tell us what the radius is;

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...and in a circle, here is the diameter -- the radius is just half of it. So if diameter is 10

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half is 5.

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Now just plug in the numbers.

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It's pi times 5 times the square root quantity of 5 squared plus 12 squared which simplifies to

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5 pi times the square root quantity 25 plus 144 or 169 -- and ooh magic number --

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169 should trigger a bell in your head.

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It is 13 squared.

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So we have 5 times pi times 13 -- 5 times 13 is 65 so the answer is 65 pi.

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Answer D.

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