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Unformatted text preview: an do the same thing here. x ln 7 ln 9
=
ln 7 ln 7
ln 9
x=
ln 7
Now, that is technically the exact answer. However, in this case it’s usually best to get a decimal
answer so let’s go one step further. x= ln 9 2.19722458
=
= 1.12915007
ln 7 1.94591015 Note that the answers to these are decimal answers more often than not.
Also, be careful here to not make the following mistake. 1.12915007 = ln 9
æ9ö
¹ ln ç ÷ = 0.2513144283
ln 7
è7ø The two are clearly different numbers.
Finally, let’s also use the common logarithm to make sure that we get the same answer. © 2007 Paul Dawkins 298 http://tutorial.math.lamar.edu/terms.aspx College Algebra log 7 x = log 9
x log 7 = log 9
x= log 9 0.954242509
=
= 1.12915007
log 7 0.845098040 So, sure enough the same answer. We can use either logarithm, although there are times when it
is more convenient to use one over the other.
[Return to Problems] (b) 2 4 y +1  3 y = 0
In this case we can’t just put a logarithm in front of both sides. There are two reasons for this.
First on the right side we’ve got a zero and we know from the previous section that we can’t take
the logarithm...
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 Spring '12
 MrVinh

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