To find side $ a $ use formula:

$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$

After substituting $r = \dfrac{ 8 }{ 3 }\, \text{cm}$ we have:

$$ \frac{ 8 }{ 3 }\, \text{cm} = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$ $$ \sqrt{ 3 } \cdot a = \frac{ 8 }{ 3 }\, \text{cm} \cdot 2 $$ $$ \sqrt{ 3 } \cdot a = \frac{ 16 }{ 3 }\, \text{cm} $$ $$ a = \dfrac{ \frac{ 16 }{ 3 }\, \text{cm} }{ \sqrt{ 3 } } $$ $$ a = \frac{ 16 \sqrt{ 3}}{ 9 }\, \text{cm} $$

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