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Pyramids

February 19, 2020

We are building pyramids with a volume of 300cm^3. We saw that each of the pyramids can be poured 3 times into the prism with the same base and height.

We made plans, decided dimensions, and then we drew out the pieces and cut them and taped them together.

We ended up with pyramids that were often incorrect! This one for example, was supposed to be 10cm by 10cm by 9cm tall. But the height was just over 7cm tall.

To understand what went wrong, we need to look at a few things. Here’s a pyramid. The height of the pyramid is the black pipe cleaner. The base of the pyramid is the pink pipe cleaner. The slant height (génératrice) is the orange pipe cleaner. Together these dimensions create a right angle triangle, and we need to use Pythagorean theorem to calculate the slant height, and use that dimension as the height of each of the triangle sides. Many of us used the pyramid height as the height of each side triangle, which results in a pyramid that is too short.

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