1) A = 9√3 = l²√3/4 => l² = 9·4·√3/√3 = 36 => l = √36 = 6 cm => P = 3·l = 18 cm
2) A = d₁·d₂/2 = 16·12/2 = 96 cm²
3) Ahexagon = 3 l²√3/2 = 3R²√3/2 = 3·25√3/2 = 75√3/2