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More on Reverse Triangle Inequality in Inner Product Spaces

Functional Analysis 2021-07-23 v1

Abstract

Refining some results of S. S. Dragomir, several new reverses of the generalized triangle inequality in inner product spaces are given. Among several results, we establish some reverses for the Schwarz inequality. In particular, it is proved that if aa is a unit vector in a real or complex inner product space (H;<.,.>)(H;< .,.>), r,s>0,p(0,s],D={xH,rxsap},x1,x2D{0}r, s>0, p\in(0,s], D=\{x\in H,\|rx-sa\|\leq p\}, x_1, x_2\in D-\{0\} and αr,s=min{r2xk2p2+s22rsxk:1k2} \alpha_{r,s}=\min\{\frac{r^2\|x_k\|^2-p^2+s^2}{2rs\|x_k\|}: 1\leq k\leq 2 \}, then x1x2Re<x1,x2>(x1+x2)2αr,s.\frac{\|x_1\|\|x_2\|-Re< x_1,x_2>}{(\|x_1\|+\|x_2\|)^2}\leq \alpha_{r,s}.

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Cite

@article{arxiv.math/0506198,
  title  = {More on Reverse Triangle Inequality in Inner Product Spaces},
  author = {Arsalan Hojjat Ansari and Mohammad Sal Moslehian},
  journal= {arXiv preprint arXiv:math/0506198},
  year   = {2021}
}

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12 pages