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Description:
ACT Math Plane Geometry Drill 2, Problem 5. What is the surface area of a rigid circular cone with diameter = 10 and height = 12?
Transcript
- 00:02
Here's your shmoop du jour.
- 00:04
What is the surface area of a rigid circular cone with diameter = 10 and height = 12?
- 00:12
And here are the potential answers...
- 00:15
Okay, it's yet another formula trivia contest.
- 00:19
So the formula is....
Full Transcript
- 00:21
surface area equals pi times r times the square root of the quantity radius squared plus height squared.
- 00:27
Well, they give us the height. Now we need the diameter to tell us what the radius is;
- 00:32
...and in a circle, here is the diameter -- the radius is just half of it. So if diameter is 10
- 00:38
half is 5.
- 00:41
Now just plug in the numbers.
- 00:43
It's pi times 5 times the square root quantity of 5 squared plus 12 squared which simplifies to
- 00:49
5 pi times the square root quantity 25 plus 144 or 169 -- and ooh magic number --
- 00:58
169 should trigger a bell in your head.
- 01:02
It is 13 squared.
- 01:04
So we have 5 times pi times 13 -- 5 times 13 is 65 so the answer is 65 pi.
- 01:11
Answer D.
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