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\mathrm{LS}=\sum_{\mathrm{i}=1}^{\mathrm{n}} \mathrm{f}\left(\mathrm{m}_{\mathrm{i}}\right) \Delta \mathrm{x}=\sum_{\mathrm{i}=1}^{\mathrm{n}}\left\{\frac{2}{\mathrm{n}}^{(\mathrm{i}-1)}\right\}^{3} \frac{2}{\mathrm{n}}=\frac{2}{\mathrm{n}} \frac{8}{\mathrm{n}^{3}}\left\{\sum_{\mathrm{i}=1}^{\mathrm{n}} \mathrm{i}^{3}-3 \sum_{\mathrm{i}=1}^{\mathrm{n}} \mathrm{i}^{2}+3 \sum_{\mathrm{i}=1}^{\mathrm{n}} \mathrm{i}-\sum_{\mathrm{i}=1}^{\mathrm{n}} 1\right\}