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\mathrm{a}=5: \mathrm{x}^{2}+\left.\frac{2}{5} \arctan \left(\frac{\mathrm{x}}{5}\right)\right|_{1} ^{3}=8+\frac{2}{5}\left\{\arctan \left(\frac{3}{5}\right)-\operatorname{acrtan}\left(\frac{1}{5}\right)\right\}