STEP 1: find side $ a $
To find side $ a $ use formula:
$$ s = \sqrt{ 3 } \cdot a $$After substituting $s = 0.25\, \text{cm}$ we have:
$$ 0.25\, \text{cm} = \sqrt{ 3 } \cdot a $$ $$ a = \dfrac{ 0.25\, \text{cm} }{ \sqrt{ 3 } } $$ $$ a \approx 0.1443\, \text{cm} $$STEP 2: find diagonal $ d $
To find diagonal $ d $ use formula:
$$ d = 2 \cdot a $$After substituting $a = 0.1443\, \text{cm}$ we have:
$$ d = 2 \cdot 0.1443\, \text{cm} $$ $$ d \approx 0.2887\, \text{cm} $$