s219
Super Member
- Joined
- Dec 7, 2011
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- 8,608
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- Virginia USA
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None of the plane geometry formulas will work for this one. The slope of the 21' ends are equal but the slopes of the 55' sides are different. Because of this, you can't just use the average heights.
You know, I went back and derived it with variables in place of the numbers, and I get the same formula when I break it into simpler volumes as I get when using the average height. It holds true whether the top is a single plane or two planar triangles. If I was a mathematician I could probably explain why, but since I'm an engineer I can just say that's rather interesting .