STEP 1: find side $ a $
To find side $ a $ use formula:
$$ A = \dfrac{ 3 \sqrt{ 3 } \cdot a^2 }{ 2 }$$After substituting $ A = 100 $ we have:
$$ 100 = \dfrac{ 3 \sqrt{ 3 } \cdot a^2 }{ 2 }$$ $$ 100 \cdot 2 = 3 \sqrt{ 3 } \cdot a^2 $$ $$ 200 = 3 \sqrt{ 3 } \cdot a^2 $$ $$ a^2 = \dfrac{ 200 }{ 3 \sqrt{ 3 } } $$ $$ a^2 = \frac{ 200 \sqrt{ 3}}{ 9 } $$ $$ a = \sqrt{ \frac{ 200 \sqrt{ 3}}{ 9 } } $$$$ a \approx 6.204 $$STEP 2: find incircle radius $ r $
To find incircle radius $ r $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $ a = 6.204 $ we have:
$$ r = \dfrac{ \sqrt{ 3 } \cdot 6.204 }{ 2 } $$$$ r = \dfrac{ 10.7457 }{ 2 } $$ $$ r \approx 5.3728 $$