STEP 1: find side $ a $
To find side $ a $ use formula:
$$ d = 2 \cdot a $$After substituting $ d = 12 $ we have:
$$ 12 = 2 \cdot a $$ $$ a = \dfrac{ 12 }{ 2 } $$ $$ a = 6 $$STEP 2: find diagonal $ s $
To find diagonal $ s $ use formula:
$$ s = \sqrt{ 3 } \cdot a $$After substituting $ a = 6 $ we have:
$$ s = \sqrt{ 3 } \cdot 6 $$ $$ s = 6 \sqrt{ 3 } $$