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Intermediate Algebra – Student Workbook – Second Edition 2013

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Lesson 4b <strong>–</strong> More on Logarithms<br />

Mini-Lesson<br />

Using Calculators to Compute with Bases other than 10<br />

Now that we know something about working with logarithms, let’s see how our calculator can<br />

help us with more complicated examples.<br />

Problem 2<br />

MEDIA EXAMPLE <strong>–</strong> INTRODUCING CHANGE OF BASE FORMULA<br />

Let’s try to compute log 2<br />

19. To start, let’s estimate values for this number. Try to find the two<br />

consecutive (one right after the other) whole numbers that log 2<br />

19 lives between.<br />

____________ < log 2<br />

19 < _____________<br />

____________ < log 2<br />

19< _____________<br />

So, now we have a good estimate for log 2<br />

19let’s see how our calculator can help us find a<br />

better approximation for the number.<br />

To compute log 2<br />

19 in your calculator, use the following steps: Log>19)>/Log2)>ENTER and<br />

round to three decimals to get:<br />

log 2<br />

19= _____________<br />

Do we believe this is a good approximation for log 2<br />

19? How would we check?<br />

____________________<br />

So, our estimation for log 2<br />

19 is good and we can say log 2<br />

19 = __________ with certainty.<br />

How did we do that again? We said that log 2<br />

19 = log(19) . How can we do that for any<br />

log(2)<br />

problem?<br />

Change of Base Formula <strong>–</strong> Converting with Common Logarithms (base 10)<br />

log b<br />

x = log(x)<br />

log(b)<br />

Scottsdale Community College Page 164 <strong>Intermediate</strong> <strong>Algebra</strong>

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