Difference between revisions of "Figurate numbers"

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Most of us are familiar with triangular numbers, such as the arrangement of ten bowling pins in a triangle,
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#REDIRECT [[Activities/TurtleArt/Tutorials/Figurate_Numbers]]
 
 
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or square numbers,
 
 
 
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but we don't necessarily know how their arithmetic works, or whether we can do the same with, say, pentagons.
 
 
 
Can we learn something by telling a turtle how to make these numbers? Let's try.
 
 
 
==Linear numbers==
 
 
 
Before we get to triangles, squares, and so on, we need to have a few tools, such as those provided in the [[Activities/TurtleArt/Tutorials/Counting|Counting]] tutorial, so that we can create figures and post notes about them. Then we can add a few more things.
 
 
 
Two-sided polygons may or may not be allowed in a particular geometry, but they are not of interest here, because both sides are necessarily of the same length.
 
 
 
[[File:TACounting.png]]
 
 
 
==Triangles==
 
 
 
What should we add? How about making dots of different colors, and providing notes about how many of each, plus the running total? Easy-peasy. We just need to do the arithmetic to work out where to put everything.
 
 
 
[[File:TATriangularNumbers.png]]
 
 
 
[[File:TATriangularNumbersProgram.png]]
 
 
 
A problem that TA can't solve for us directly is the formula for triangular numbers. Gauss figured it out on his own as a child, but the rest of us need a hint, at least. Here is a big hint.
 
 
 
[[File:TATriangularNumberFormulaHint.png]]
 
 
 
The area of a rectangle can be written Base × Height. The area of a right triangle is half the area of a rectangle with the same Base and Height. Can you do the rest?
 

Latest revision as of 00:31, 14 July 2011