Solve the equation ##x^\frac{17}{6} + x^\frac{21}{25} =15##

AI Thread Summary
The discussion focuses on solving the equation x^(17/6) + x^(21/25) = 15, exploring various methods such as Newton's method, Brent's method, and Halley's method for their effectiveness. Participants note that Newton's method is efficient, while also questioning the reliability of Brent's and Halley's methods. Excel's goal seek feature is mentioned as a quick setup option, though it may complicate larger calculations. The conversation emphasizes the need for general methods to address equations with fractional exponents. Overall, the thread highlights the search for robust numerical solutions to complex equations.
chwala
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Homework Statement
Solve the equation ##x^\frac{17}{6} + x^\frac{21}{25} =15##

This is my original question (set by me).
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What about Brent's method and Halley's method? Are they reliable? I don't hear much about them.
 
Excel goal seek is quick to set up EDIT: but may be more difficult to incorporate into a bigger calc

$$\begin{array}{|c|c|c|c|}
\hline X&X**(17/6)&X**(21/25)&sum \\
\hline 2.463664029&12.86710567&2.132693501&14.99979917 \\
\hline
\end{array}$$
 
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Essentially I just have this problem that I'm stuck on, on a sheet about complex numbers: Show that, for ##|r|<1,## $$1+r\cos(x)+r^2\cos(2x)+r^3\cos(3x)...=\frac{1-r\cos(x)}{1-2r\cos(x)+r^2}$$ My first thought was to express it as a geometric series, where the real part of the sum of the series would be the series you see above: $$1+re^{ix}+r^2e^{2ix}+r^3e^{3ix}...$$ The sum of this series is just: $$\frac{(re^{ix})^n-1}{re^{ix} - 1}$$ I'm having some trouble trying to figure out what to...
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