r_{m} = \sqrt{a_{2}^{2} + (\frac{D}{2})^{2}} = \sqrt{0, 1^{2} + 0, 01^{2}} = 0, 1005 m

${r_m=\sqrt{a_2^2+ \bigg(\frac{D}{2}\bigg)^2}=\sqrt{0,1^2+0,01^2 }=0,1005\, \mathrm{m}}$

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