#9 ^ x = x

12 messages · Page 1 of 1 (latest)

low parcel
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solve for x

formal needle
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This equation has no real solution

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Define $f(x) := 9^x - x$, then $f'(x) = \ln(9) \cdot 9^x - 1$.

burnt sparrowBOT
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ℝafain

formal needle
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Hence
$$f'(x)
\begin{cases}
<0&\text{ if }x<-\frac{\ln(\ln(9))}{\ln(9)}\
=0&\text{ if }x=-\frac{\ln(\ln(9))}{\ln(9)}\

0&\text{ if }x=-\frac{\ln(\ln(9))}{\ln(9)}
\end{cases}$$

burnt sparrowBOT
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ℝafain

formal needle
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Hence $f$ is minimum at $-\frac{\ln(\ln(9))}{\ln(9)}$, where its value is $\frac{1+\ln(\ln(9))}{\ln(9)} > 0$.

burnt sparrowBOT
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ℝafain

formal needle
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Hence $f$ does not attain zero anywhere in $\mathbb R$.

burnt sparrowBOT
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ℝafain

normal remnant
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the solution in C can be defined as follows:
-(W(-2ln(3)))/(2ln(3))

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I love W Lambert tbh