To find incircle radius $ r $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $a = 0.5\, \text{cm}$ we have:
$$ r = \dfrac{ \sqrt{ 3 } \cdot 0.5\, \text{cm} }{ 2 } $$$$ r = \dfrac{ 0.866\, \text{cm} }{ 2 } $$ $$ r \approx 0.433\, \text{cm} $$