[tex]\it a_6=\dfrac{R\sqrt3}{2} = 9 \Rightarrow R=9\cdot\dfrac{2}{\sqrt3} = \dfrac{9\cdot2\sqrt3}{3} = 6\sqrt3\ cm
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\ell_6=R = 6\sqrt3 \ cm
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\mathcal{A}_{hex} = 6\cdot\dfrac{\ell^2\sqrt3}{4} = 6\cdot\dfrac{(6\sqrt3)^2\sqrt3}{4} =6\cdot\dfrac{36\cdot3\sqrt3}{4} = 162\sqrt3\ cm^2[/tex]
[tex]\it \ell_4 = R\sqrt2 = 6\sqrt3\cdot\sqrt2 =6\sqrt6\ cm
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a_4 = \dfrac{\ell_4}{2} = \dfrac{6\sqrt6}{2} = 3\sqrt6\ cm[/tex]