“parallelogram law”的概念、定义、翻译、参考文献-科学参考

单词	parallelogram law
释义	parallelogram law Mathematics This law states for a parallelogram that the sum of the squares of the diagonals’ lengths equals the sum of the squares of the sides’ lengths. Parallelograms are the only quadrilaterals for which the law holds. For a parallelogram OABC, where OA = v and OC = w, the law states $\| v + w \|^{2} + \| v - w \|^{2} = 2 \| v \|^{2} + 2 \| w \|^{2} .$ This identity holds in inner product spaces; a Banach space is a Hilbert space if and only if the parallelogram law holds.
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