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$\small\text{Quadrato:}$
$\small\text{lato } l= \dfrac{d}{\sqrt2} = \dfrac{30\cancel{\sqrt2}}{\cancel{\sqrt2}} = 30\,cm;$
$\small\text{area } A= l^2 = 30^2 = 900\,cm^2.$
$\small\text{Triangolo equilatero equivalente al quadrato:}$
$\small\text{area } A= 900\,cm^2;$
$\small \text{lato conoscendo l'area:}$
$\small l= \sqrt{\dfrac{2A}{\dfrac{\sqrt3}{2}}} $
$\small l= \sqrt{2·900·\dfrac{2}{\sqrt3}} $
$\small l= \sqrt{1800·\dfrac{2}{\sqrt3}} $
$\small l= \sqrt{\dfrac{3600}{\sqrt3}} \approx{45,59}\,cm; $
$\small\text{perimetro:} 2p= 3·l = 3·45,59 \approx{136,8}\,cm.$
quadrato
lato = 30√2 / √2 = 30 cm
area A = lato^2 = 30^2 = 900 cm^2
triangolo
area A' = A = 900 cm^2 = 0,433*lato^2
lato = √900/0,433 = 45,6 cm
perimetro = 3*lato = 136,8 cm