English

An identity for $(-q^{5};\,q^{10})_{\infty}$

General Mathematics 2021-11-24 v1

Abstract

We prove that n=0(1+q10n+5)=n=qn2n=(1)n(q)n(3n1)/24n0(q)n(n+1)2sin{(2n+1)3π10}n0(q)n(n+1)2sin{(2n+1)π10}q<1 \prod_{n=0}^{\infty}(1+q^{10n+5}) = \frac{\sum_{n=-\infty}^{\infty}q^{n^{2}}\, \sum_{n=-\infty}^{\infty}(-1)^{n}\, (-q)^{n(3n-1)/2}}{4\, \sum_{n\geq 0}(-q)^{\frac{n(n+1)}{2}}\sin \left\{\frac{(2n+1)3\pi}{10}\right\}\, \sum_{n\geq 0}(-q)^{\frac{n(n+1)}{2}}\sin \left\{\frac{(2n+1)\pi}{10}\right\}} \qquad |q|<1 using identities due to Ramanujan.

Cite

@article{arxiv.2111.11857,
  title  = {An identity for $(-q^{5};\,q^{10})_{\infty}$},
  author = {Sumit Kumar Jha},
  journal= {arXiv preprint arXiv:2111.11857},
  year   = {2021}
}

Comments

3 pages

R2 v1 2026-06-24T07:48:53.878Z