STEP 1: find side $ a $
To find side $ a $ use formula:
$$ d = 2 \cdot a $$After substituting $ d = 100 $ we have:
$$ 100 = 2 \cdot a $$ $$ a = \dfrac{ 100 }{ 2 } $$ $$ a = 50 $$STEP 2: find incircle radius $ r $
To find incircle radius $ r $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $ a = 50 $ we have:
$$ r = \dfrac{ \sqrt{ 3 } \cdot 50 }{ 2 } $$$$ r = \dfrac{ 50 \sqrt{ 3 } }{ 2 } $$ $$ r = 25 \sqrt{ 3 } $$