Review Day for Exponential/Log Function Unit

Published on: **Mar 3, 2016**

Published in:
Technology Education

- 1. What Smarty-Pants InventedLogarithms and Why the #@&% Did He Do So?!John Napier is the Scottish guytraditionally credited for theinvention of logarithms as he wasthe first to publish his discoveriesin a book called MirificiLogarithmorum Canonis Descriptio(Description of the Wonderful Ruleof Logarithms) in 1614. One of hisgoals was to simplify the “tedious”tasks of multiplication, division, androot-finding of numbers by meansof tables of common logarithms(remember, there were nocalculators yet).
- 2. Here’s the idea. Let’ssay we want to multiply9.73x0.871. Would youwant to do this by hand?Napier didn’t think so.So, he came up with thisgame plan. Use thechart provided (thatNapier helped create) towork out themultiplication problem.
- 3. Notice all our x’s are between 5.6 and 9.99 (this is not a complete chart—we’re missing numbers 1 to 5.59) Were going to need to rewrite 0.871 as Since exponential and logarithmic functions are inverses of each other, we know that Convert to log form to convince yourself: So,
- 4. Look up these logs to simplify: 10log9.73x10log8.71x10-1= Combine the exponents to get: (Remember, no calculators allowed!) Convert to log form: Now find which x corresponds to this log: Go ahead and pull out your calculator now to see how close we got:
- 5. Preface to Description of the Wonderful Rule of Logarithms: (Totally worth the read. Trust me on this one.) Since nothing is more tedious, fellow mathematicians, in the practice of the mathematical arts, than the greatdelays suffered in the tedium of lengthy multiplications and divisions, the finding of ratios, and in the extraction of square and cube roots– and in which not only is there the time delay to be considered, but also the annoyance of the many slippery errors that can arise: I had therefore been turning over in my mind, by what sure and expeditious art, I might be able to improve upon these said difficulties. In the end after muchthought, finally I have found an amazing way of shortening the proceedings, and perhaps the manner in which the method arose will be set out elsewhere: truly, concerning all these matters, there could be nothing more useful than the method that I have found. For all the numbers associated with the multiplications, and divisions of numbers, and with the long arduous tasks of extracting square and cube roots are themselves rejected from the work, and in their place other numbers are substituted, which perform the tasks of these rejected by means of addition, subtraction, and division by two or three only. Since indeed the secret is best made common to all, as all good things are, then it is a pleasant task to set out the method for the public use of mathematicians. Thus, students of mathematics, accept and freely enjoy this work that has been produced by my benevolence. Farewell. Translation by Ian Bruce
- 6. First edition of Napier’s book; currently going for upwards of $30,000 online
- 7. So why is it called a “logarithm” anyway?LOGARITHMfrom Greek logos and arithmoslogos: word, reasoning, ratio, proportionarithmos: numberA logarithm is literally a "reasoning number" Sources: mathforum.org and dictionary.com
- 8. Now for some review before the test. Pick a group. Pick a problem.ONE: How many times would you have to fold a paper (of normal thickness)onto itself in order to reach the moon?TWO: Your first day of work, you make 2 pennies and every day after that your wage doubles. Onwhat day do you make a million dollars?THREE: Ants are invading! There are two ants on Union’s football field and theyre ready to buildan army to try to reach across the entire field. Initially there were two ants, and every hour, theyreable to bring more friends and double their army. In how many hours will there be enough ants tostretch across the entire field?FOUR: Remember our game of Jeopardy!? All students started with 100 points and had thechance to double their score each round. Let’s say you’re a big risk taker in addition to beingawesome at math and you, indeed, double your score each round. After which round will yousurpass one hundred million points?