Monthly Archives: March 2013

Divisibility by 17

I thought that a test for divisibility by 17 ought to work like the test for divisibility by 13 that I described in my last post.  No such luck.  But something similar does work. And here is a rough explanation why the method works.

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Divisibility Test for Thirteen

My department chair, Sherry Ettlich, sent us a link to this video which shows a quick (new?) method of determining if a number is divisible by 7. After I figured out how it worked, it occurred to me to try the same … Continue reading

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Math Makes Me Happy

I wrote previously about how I love math and it makes me sad.  This article, Physics, Logic, Topology and Computation: A Rosetta Stone by John C. Baez and Mike Stay makes me very happy especially the table on page 66 and … Continue reading

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What to Know About a Function

When I introduce the concept of function in my college algebra class, I emphasize that the formula is not enough.  To really know a function is to know its formula and its shape (graph) and its domain and range and … Continue reading

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Completing the Square Versus The Quadratic Formula

My college algebra class is learning to find the zeros of polynomial functions, so we are solving lots of quadratic equations.  If the quadratic expression is not easily factorable, I have been saying. “Just use the Quadratic Formula.”  Here is … Continue reading

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