natural log problem

lowend

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Joined
Feb 4, 2011
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4
The function is P = 12 + 20ln(x)

P = 90 is given so,

90 = 12 + 20ln(x)

and they want to solve for x. Logs have always given me problems. I can solve for P if x is given but don't know where to start on this one.

Thanks so much!
Steve
 
Hello, Steve!

\(\displaystyle \text{Given: }\:p \,=\, 12 + 20\ln x,\,\text{ and }P = 90\)

\(\displaystyle \text{Solve for }x.\)

\(\displaystyle \text{We have: }\;12 + 20\ln x \:=\:90 \quad\Rightarrow\quad 20\ln x \:=\:78 \quad\Rightarrow\quad \ln x \,=\,\tfrac{78}{20} \,=\,3.9\)

\(\displaystyle \text{Therefore: }\;x \:=\:e^{3.9} \;\approx\;49.4\)

 
Thanks! It's funny how simple problems like this can trip me up. I'm so glad I found this place :)
 
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