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OpenStudy (anonymous):
n(x+5)=ln(x-1)-ln(x+1)
solve the logarithmic function algebraically. round the result to three decimal places.
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OpenStudy (jamesj):
ok, what is ln a + ln b equal to?
OpenStudy (jamesj):
ln a + ln b = ...what?
OpenStudy (anonymous):
lnc?
OpenStudy (jamesj):
ln a + ln b = ln(ab)
ln a - ln b = ... what?
OpenStudy (anonymous):
ln a-ln b= ln a divided by b?
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OpenStudy (jamesj):
ln a - ln b = ln(a/b) yes
Last identity before we solve your problem. If
ln p = ln q
what can we say about p and q?
OpenStudy (anonymous):
umm they can be multiplied or divide? idk
OpenStudy (jamesj):
If
ln p = ln q
then
p = q
OpenStudy (jamesj):
Now, your problem:
ln(x+5)=ln(x-1)-ln(x+1)
Using the identity we wrote down above, what is
ln(x-1)-ln(x+1) = ... ?
OpenStudy (anonymous):
lnx-1/lnx+1?
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OpenStudy (jamesj):
No.
ln a - ln b = ... what?
OpenStudy (anonymous):
ln(a/b)
OpenStudy (jamesj):
ln a - ln b = ln(a/b).
hence
ln(x-1)-ln(x+1) = ... what?
OpenStudy (anonymous):
ln(x-1/x+1)?
OpenStudy (jamesj):
Yes. Now
\[ \ln(x+5)=\ln(x-1) - \ln(x+1) = \ln ( \frac{x-1}{x+1} ) \]
which implies
\[ x + 5 = \frac{x-1}{x+1} \]
Now solve for x.
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OpenStudy (anonymous):
ok thank yu so much
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