Proving x^x=4: A Brain Teaser with Multiple Solutions | Homework Help

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SUMMARY

The equation x^x=4 has a definitive solution: x=2. Despite initial assumptions of multiple solutions, analysis using the Newton-Raphson method confirms convergence to this single solution. Logarithmic differentiation reveals that the function has only one critical point at x=1/e, reinforcing that x=2 is the only solution. Therefore, any claims of additional solutions are incorrect.

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Homework Statement


[tex]x^x=4[/tex]

this is a brain teaser a co-worker gave me. I can take the ln of bothb sides... etc but it ends up going in a circle. any guidance on this problem? I know one solution is 2 but he said there is at least one more solution.
 
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ssb said:
I know one solution is 2 but he said there is at least one more solution.
He's incorrect; the only solution to the equation is x=2. I can't think of an elegant proof right now, but you could use the Newton-raphson method and observe that no matter your choice for intial solution, the algorithm will always converge to 2.
 
Using logarithmic differentiation, you can show that the function has only a single critical point (a minimum) at x = 1/e. By observation, x = 2 is a solution. Since there are no other critical points, this must be the only solution.
 
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