Division of fractions is generally taught in elementary grades by the rule, "invert and multiply." But why does this work? It can be explained formally by the field axioms, but that doesn't help demystify the rule for 4th or 5th graders. A while back I was asked why this rule works and I realized it was never explained to me as a student. After some thought, here is what I came up with. I hope it helps.
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https://www.youtube.com/watch?v=jttBH_93czc
3-D demonstration of the motions of the sun and moon in the sky, created using Visual Python (VPython).
[By the way, given the number of clueless comments, it seems I must point out, this simulation HAS ABSOLUTELY NOTHING TO DO WITH THE MIND NUMBINGLY LUNATIC FLAT EARTH "THEORY" NONSENSE!!! (Don't waste my time.) This is about the apparent sky for a localized observer: a phenomenological perspective one has for observational astronomy or navigation. (Go outside and look up!) When you stand on the ground and see a few hundred yards, the earth appears locally flat. You lack depth perception for cosmic distances because your eyes are close together compared to the distances involved. That's why the sun, moon, and stars appear to be at the same distance. When everything in the cosmos appears the same distance away, it gives the illusion that they all lie on a sphere centered on the observer. Hence the sphere of the sky is an illusion. This simulation is about understanding this localized perspective.]
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https://www.youtube.com/watch?v=5k--My8fnes
Hewlitt Packard introduced their HP 35 in 1972. It was the world's first scientific calculator. It could be considered a little geeky in that it forced the user to learn a data entry system known as Reverse Polish Notation (RPN), which was closer to the way the internal computer chip handled the process. What thousands of scientists and engineers discovered, however, was that this data entry system was closer to the way their brains processed the problems too. RPN is addictive. If any serious science or math student asks my recommendation on a calculator, RPN is it. The HP 35s was issued on the 35th anniversary of the original HP 35.
Please HP...keep RPN alive.
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https://www.youtube.com/watch?v=cPKg_JtI-Ys
The basic area formulas presented as reasoned methods rather than formulas to be memorized. Part 4 shows the derivation of the surveyor's method for finding the area of an arbitrary polygon or an arbitrary curve that can be approximated as a polygon.
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https://www.youtube.com/watch?v=uKHIkvU5BXI