STEP 1: find side $ a $
To find side $ a $ use formula:
$$ d = 2 \cdot a $$After substituting $ d = 90 $ we have:
$$ 90 = 2 \cdot a $$ $$ a = \dfrac{ 90 }{ 2 } $$ $$ a = 45 $$STEP 2: find diagonal $ s $
To find diagonal $ s $ use formula:
$$ s = \sqrt{ 3 } \cdot a $$After substituting $ a = 45 $ we have:
$$ s = \sqrt{ 3 } \cdot 45 $$ $$ s = 45 \sqrt{ 3 } $$