Intereting Posts

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Summation of series $\sum_{n=1}^\infty \frac{n^a}{b^n}$?
Why do $2^{\lt\kappa}=\kappa$ and $\kappa^{\lt\kappa}=\kappa$ when the Generalized Continuum Hypothesis holds?
Find $\int e^{2\theta} \cdot \sin{3\theta} \ d\theta$
How to solve $a_n = 2a_{n-1} + 1, a_0 = 0, a_1 = 1$?
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Literature suggestions: Stochastic Integration; for intuition; for non-mathematicians.
How to find the sum of the sequence $\frac{1}{1+1^2+1^4} +\frac{2}{1+2^2+2^4} +\frac{3}{1+3^2+3^4}+…$
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If $a_1,a_2,\ldots, a_n$ are distinct primes, and $a_1=2$, and $n>1$, then $a_1a_2\cdots a_n+1$ is of the form $4k+3$.
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Archimedean places of a number field

The following result discussed by Ramanujan is very famous: $$\sqrt[3]{\sqrt[3]{2} – 1} = \sqrt[3]{\frac{1}{9}} – \sqrt[3]{\frac{2}{9}} + \sqrt[3]{\frac{4}{9}}\tag {1}$$ and can be easily proved by cubing both sides and using $x = \sqrt[3]{2}$ for simplified typing.

Ramanujan established many such denesting of radicals such as $$\sqrt{\sqrt[5]{\frac{1}{5}} + \sqrt[5]{\frac{4}{5}}} = \sqrt[5]{1 + \sqrt[5]{2} + \sqrt[5]{8}} = \sqrt[5]{\frac{16}{125}} + \sqrt[5]{\frac{8}{125}} + \sqrt[5]{\frac{2}{125}} – \sqrt[5]{\frac{1}{125}}\tag {2}$$$$\sqrt[3]{\sqrt[5]{\frac{32}{5}} – \sqrt[5]{\frac{27}{5}}} = \sqrt[5]{\frac{1}{25}} + \sqrt[5]{\frac{3}{25}} – \sqrt[5]{\frac{9}{25}}\tag {3}$$$$\sqrt[4]{\frac{3 + 2\sqrt[4]{5}}{3 – 2\sqrt[4]{5}}} = \frac{\sqrt[4]{5} + 1}{\sqrt[4]{5} – 1}\tag{4}$$$$\sqrt[\color{red}6]{7\sqrt[3]{20} – 19} = \sqrt[3]{\frac{5}{3}} – \sqrt[3]{\frac{2}{3}}\tag{5}$$$$\sqrt[6]{4\sqrt[3]{\frac{2}{3}} – 5\sqrt[3]{\frac{1}{3}}} = \sqrt[3]{\frac{4}{9}} – \sqrt[3]{\frac{2}{9}} + \sqrt[3]{\frac{1}{9}}\tag{6}$$

$$\sqrt[8]{1+\sqrt{1-\left(\frac{-1+\sqrt{5}}{2}\right)^{24}}} = \frac{-1+\sqrt{5}}{2}\,\frac{1+\sqrt[4]{5}}{\sqrt{2}}\tag{7}$$

- the sum of a series
- Inverting the Cantor pairing function
- How to solve this logarithm inequality with absolute value as its base?
- Given 4 integers, $a, b, c, d > 0$, does $\frac{a}{b} < \frac{c}{d}$ imply $\frac{a}{b} < \frac{a+c}{b+d} < \frac{c}{d}$?
- Guessing one root of a cubic equation for Hit and Trial
- Solving system of multivariable 2nd-degree polynomials

with the last one found in *Ramanujan’s Notebooks*, Vol 5, p. 300. Most of these radical expressions are **units** (a unit is an algebraic integer $\alpha$ such that $\alpha\beta = 1$ where $\beta$ is another algebraic integer).

For me the only way to establish these identities is to raise each side of the equation to an appropriate power using brute force algebra and then check the equality. However for higher powers (for example equation $(2)$ above) this seems very difficult.

Is there any underlying structure in these powers of units which gives rise to such identities or these are mere strange cases which were noticed by Ramanujan who used to play with all sorts of numbers as a sort of hobby? I believe (though not certain) that perhaps Ramanujan did have some idea of such structure which leads to some really nice relationships between units and their powers. I wonder if there is any sound theory of such relationships which can be exploited to give many such identities between nested and denested radicals.

- How to solve $x^3=-1$?
- Why is negative times negative = positive?
- How do I isolate $y$ in $y = 4y + 9$?
- Why are the domains for $\ln x^2$ and $2\ln x$ different?
- Basic trigonometry identities question
- Prove that $\frac{1}{2}+\frac{2}{2^2}+\frac{3}{2^3} +…+ \frac{n}{2^n} = 2 - \frac{n+2}{2^n} $
- Prove the following property of $f(x)$?
- An inequality involving two complex numbers
- How can I write an equation that matches any sequence?
- Prove that $x^2<\sin x \tan x$ as $x \to 0$

We also have the following identity,

$$\sqrt[3]{m^3-n^3+6m^2n+3mn^2-3(m^2+mn+n^2)\sqrt[3]{mn(m+n)}}=\\ \sqrt[3]{m^2(m+n)}-\sqrt[3]{mn^2}-\sqrt[3]{(m+n)^2n}$$

For $m=n=1$ we get $(1)$.

For $m=4$ and $n=1$ we get $(5)$.

I found a PDF, where the authors have working algorithms to denest nested radicals like that of Ramanujan’s, *without the use of Galois theory*.

https://www-old.cs.uni-paderborn.de/uploads/tx_sibibtex/DenestRamanujansNestedRadicals.pdf

I think this might help in offering an alternative way, regarding relations in the form of algorithms, to simplify and denest nested radicals as opposed to the helpful links given in the comments to your question. It is certainly detailed and interesting, so I hope it’s of some use to you.

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